Centre for Mathematics, University of Coimbra

Seminars - Historic

Structure-preserving integrators in Poisson geometry

2024-01-15

Speaker: Oscar Cosserat (Univ. Gottingen, Germany)

A geometric integrator is a numerical method that preserves the geometric properties of the flow of a differential equation. The rise of geometric integrators stems from the geometrization of mechanics and the development of numerical analysis. I will explain here their relevance within the...

A brief introduction to Machine Learning: from the perceptron to large language models

2023-12-15

Speaker: Francisco Pereira (CISUC & Polytechnic Institute of Coimbra)

The field of machine learning has experienced a strong expansion in recent years, mostly driven by the development of new computational methods and the unprecedented surge in the volume of data accessible for processing and analysis. This dynamic has opened up new frontiers for exploration...

Dynamics and stability of a network human-landscape model

2023-11-24

Speaker: Ana Jacinta Soares (CMAT, Univ. Minho)

Ecological networks serve as a modern tool to explore the dynamics of interconnected, non-uniform landscape regions. We develop a mathematical model by coupling human activity with an ecological model for a network of Landscape Units (LUs). The model consists of a network of interacting...

Advances in finite volume methods for the simulation of flows in porous media

2023-11-17

Speaker: Fernando Raul Contreras (Univ. Federal de Pernambuco, Brazil)

We study linear and nonlinear finite volume methods coupled to the high order methods to simulate the behavior of flows in porous media with complex geological properties. Ideally, the linear and nonlinear methods should satisfy the following numerical properties: Preserve linearity, handle...

A low-cost algorithm to determine spacecraft trajectories in CR3BP

2023-06-23

Speaker: Sirani M. Perera (Embry-Riddle Aeronautical University, USA)

The traffic within the Cislunar region continues to grow, yielding an increasing demand for efficient techniques to determine the trajectory of a satellite in the circular restricted three-body problem (CR3BP). In this talk, we introduce a novel technique that incorporates interpolation with...

Scientific machine learning: some methods and applications

2022-12-09

Speaker:

Emmanuel Franck & Victor Michel-Dansac (Inria & IRMA, Strasbourg, France)

Machine learning performance has exploded since the beginning of the 2010s. In this talk, we propose to investigate what learning can bring in the context of scientific computing and approximation of PDEs. To that end, we will introduce two interesting frameworks:...

Scalable methods for high-dimensional inverse problems using neural networks and implicit method of moments

2022-12-02

Speaker: João M. Pereira (IMPA, Rio de Janeiro, Brazil)

I will talk about two recent projects of mine in that concern high-dimensional inverse problems. In the first project, we use machine learning tools for discovering laws and equations that govern high-dimensional datasets. Specifically, I will present two methods we...

High order methods for PDE: panorama and perspective

2022-11-11

Speaker: Stéphane Clain (CMUC, Univ. Coimbra)

Very high order methods enable to substantially reduce the computational effort while producing high accuracy approximations. They also provide high spectral resolution to catch very small structures with respect to the mesh parameter size. Three major issues have to be addressed to ...

A low-cost alternating projection approach for a continuous formulation of convex and cardinality constrained optimization

2022-10-21

Speaker: Evelin Krulikovski (Univ. Nova de Lisboa)

We consider convex constrained optimization problems that also include a cardinality constraint. In general, optimization problems with cardinality constraints are difficult mathematical programs which are usually solved by global techniques from discrete optimization. We assume that the...

Asymptotic behavior and stability of solutions in differential equations of mixed type

2022-09-23

Speaker: Sandra Pinelas (DCEE, Academia Militar)

In this study, some new results are obtained on stability analysis of a mixed type differential equation. These results were obtained by using an appropriate real root of the characteristic equation. Moreover, by the use of two appropriate distinct real roots of the...

K dissimilar paths

2022-06-24

Speaker: Marta Pascoal (Politecnico di Milano, CMUC/University of Coimbra, and INESC Coimbra)

The aim of this talk is to address the determination of K alternative paths linking two given nodes in a network. In particular the paths are expected to minimize simultaneously a linear objective function and a similarity measure based on the overlaps between them. The problem is modelled...

Recent results on planar predator-prey and competitive models with seasonality

2022-03-11

Speaker: Carlota Rebelo Gonçalves (Univ. de Lisboa)

TBA...

How can the Cerebral Aneurysms near-wall region be investigated?

2022-01-28

Speaker: Iolanda Velho (CEMAT, Univ. Lisboa)

Cerebral Aneurysms (CA) represent a frightening and silent threat with a high prevalence and mortality rate. Despite several studies, the mechanisms of aneurysm development are not fully understood. Nonetheless, hemodynamic and biochemical factors, especially related to the vessel wall, are...

A multi-scale biological description with application to autoimmune diseases

2022-01-14

Speaker:

Ana Jacinta Soares (CMAT, Univ. Minho)

Biological systems are usually described at the macroscopic level, by considering the relevant interacting populations that are involved in the system. However, it is well known that a detailed description at the cellular level could be more appropriate in understanding the complex...

Feedback control of falling liquid films using a hierarchical model approach

2021-04-16

Speaker:

Susana Gomes (Univ. Warwick, UK)

The flow of a thin film down an inclined plane is a canonical setup in fluid mechanics and associated technologies, with applications such as coating, where the liquid-gas interface should ideally be flat, and heat or mass transfer, where an increase of interfacial area is desirable. In each...

Stochastic optimization of multiple objectives and fairness in machine learning

2021-02-12

Speaker: Luís Nunes Vicente (Lehigh Univ., USA & CMUC, Univ. Coimbra)

In the application of machine learning to real life decision-making systems, e.g., credit scoring and criminal justice, the prediction outcomes might discriminate against people with sensitive attributes, leading to unfairness. The commonly used strategy in fair machine learning is to...

Symbolic data and optimization

2021-01-15

Speaker:

Paula Amaral (NOVA Univ. of Lisbon)

Today, in many areas, we collect huge volumes of data to analyse. To use this data in classification methods it is necessary to aggregate them keeping as much information as possible about the data. Histograms are a useful way of representing large sets of data keeping...

Model-based evaluation of school- and non-school based public health measures on controlling the COVID-19 pandemic in the Netherlands

2020-12-11

Speaker: Ganna Rozhnova (University Medical Center Utrecht, Netherlands)

Introduction: In autumn 2020, many countries, including the Netherlands, are experiencing a second wave of the COVID-19 pandemic. Health policymakers are struggling with choosing the right mix of measures to keep the COVID-19 case numbers under control, but still allow a minimum of social...

Complex network of epidemic models

2020-11-20

Speaker:

Cristiana J. Silva (CIDMA, Univ. Aveiro)

In this work, we consider an epidemiological model given by a system of ordinary equations, for the transmission dynamics of SARS-CoV-2, with piecewise constant parameters. Based on this model, we construct a complex network of dynamical systems, in order to take into account the...

Mathematical modelling in solid mechanics: an example with fracking

2020-11-06

Speaker: Nicolas Van Goethem (CMAFCIO, Univ. Lisboa)

I will present the various steps of mathematical modelling on a practical case: presentation and setting of the problem (hydraulic fracture), choice of the approach (energergetical and variational), choice of the method (topological differentiation), design of the algorithm (quasi-static and...

Mathematical models and methods for Breach Formation in Earth Embankment Dams

2020-09-16

Speaker: Giuseppe Romanazzi (Unicamp, Campinas, Brazil)

After an overview of breach formation in embankment dams, we present different mathematical models and methods used nowadays to predict the formation of breach in earth embankments. The strengths and weaknesses of the prediction models are discussed....

Is fractional calculus the ultimate solution to all anomalous-diffusion problems?

2020-02-28

Speaker: Luís Ferrás (Univ. do Minho)

Albert Einstein, in his work regarding Brownian motion (1905) entitled "On the motion of small particles suspended in liquids at rest required by the molecular-kinetic theory of heat", gave the definitive confirmation that atoms and molecules exist. Since then, many works have...

Optimization meets Medical Physics: tailored algorithms

2020-02-14

Speaker: Humberto Rocha (School of Economics, Univ. Coimbra)

Radiotherapy has been a fertile field for the development of algorithms to tackle the different optimization problems that arise in this area. A panoply of algorithms has been used for different problems including integer programming, linear programming or quadratic programming algorithms....

The Method of Fundamental Solutions and its application for solving shape optimization problems

2020-01-10

Speaker: Pedro Antunes (Univ. Aberta, Lisboa)

This talk is divided into two parts. In the first part we give an overview of the application of the Method of Fundamental Solutions (MFS) for solving boundary value problems with elliptic PDE's. The MFS is a meshfree method where the solution is approximated by a linear combination of...

Matrix functions: applications, computation and topics of research

2019-12-11

Speaker: João Cardoso (ISEC & CMUC)

The first known references to matrix functions can be found in the works of Cayley, Laguerre, Peano and Sylvester in the second half of the 19th century. However, just in the last decades of the 20th century we assisted to a growing interest in developing methods for the computation of...

Multiobjective optimization: fundamentals and an application in demand response

2019-12-04

Speaker: Maria João Alves (Faculty of Economics, Univ. Coimbra)

In this talk, the fundamental concepts of multiobjective optimization and scalarizing techniques to compute nondominated solutions will be introduced. Scalarizing techniques consist of transforming the original multiobjective problem into a single objective problem that may be solved...

Peregrine's system revisited

2019-03-27

Speaker: Ángel Durán (Univ. Valladolid, Spain)

In 1967, D. H. Peregrine proposed a Boussinesq-type model for long waves in shallow waters of varying depth (Peregrine, J Fluid Mech 27:815-827, 1967). This prominent paper turned a new leaf in coastal hydrodynamics along with contributions by Serre (La Houille Blanche 8:374-388, 1953) and...

The finite element method in sheet metal forming simulation

2019-02-27

Speaker: Diogo Neto (DEM, Univ. Coimbra)

Numerical simulation is an indispensable tool for the successful implementation of digital manufacturing. The actual requirements for a higher degree of product customization dictate the use of simulation, allowing the virtual testing and validation of product, process and system design....

Stochastic solutions for nonlinear partial differential equations

2019-02-20

Speaker: Rui Vilela Mendes (CMAFCIO, Univ. Lisboa)

A stochastic solution of a pde is a stochastic process that started from a point in the domain, generates a boundary measure which, when integrated over the initial condition, provides a local solution of the equation. Stochastic solutions not only provide new exact solutions for nonlinear...

Portfolio selection in evolutionary algorithms

2019-01-30

Speaker: Andreia P. Guerreiro (CISUC, DEI-UC)

Evolutionary Algorithms (EAs) are algorithms inspired on the process of natural selection, and are among the most popular methods in multiobjective optimization. One of the main steps of an EA is selection which is aimed at focusing on the best individuals, but must also maintain a...

Performance estimation of first-order methods for composite convex optimization

2018-10-18

Speaker: François Glineur (Université catholique de Louvain, Belgium)

Composite convex optimization consists in the minimization of a convex objective function equal to the sum of several convex functions with different properties, for example a smooth term and a nonsmooth term. We consider a large class of first-order methods designed to solve such...

Efficient and accurate Lagrangian-Eulerian numerical schemes for solving hyperbolic balance laws

2018-07-13

Speaker: Eduardo Abreu (UNICAMP, Brazil)

We develop first-order and high-resolution stable-fast numerical schemes for hyperbolic balance law models. A key feature is the dynamic tracing forward of the integral curves, which are locally conservative and preserve the natural setting of weak (entropic) solutions linked to the...

Numerical modelling of cell-renewal, pit patterns and crypt fission in colonic crypts

2018-07-10

Speaker: Giuseppe Romanazzi (UNICAMP, Brazil)

The colonic epithelium is filled in its internal walls by small cavities called crypts. These crypts are small tubular glands, containing proliferative cells, that obey to a programmed cell mechanism. The aberrant crypts occur as a consequence of an abnormal behavior of this programmed...

A problem-dependent inner approximation of the completely positive cone

2018-06-27

Speaker:

Mina Saee Bostanabad (PhD student, CMUC)

Motivated by the expressive power of completely positive programming and its dual, copositive programming, to encode hard optimization problems, many approximation schemes for the completely positive and copositive cones have been proposed and successfully used. For the completely positive...

Mining chemical space for pharmacological rules: corneal permeation as an example

2018-06-06

Speaker:

Rui M. M. Brito (BSIM Therapeutics, IPN & Univ. Coimbra) and João H. B. Meireles (BSIM Therapeutics, IPN)

Drug discovery and development is a complex, long and expensive process involving searches in a multidimensional space and multi-objective optimization based on apparently unrelated target functions. The discovery of a new "small molecule" medicine depends on the identification of...

Multiscale non-helical dynamos

2018-03-14

Speaker: Roman Chertovskikh (SYSTEC, Univ. Porto)

In this talk a short introduction to the magnetic dynamo theory (explaining how magnetic fields can be produced by flows of an electrically conducting fluid) as well as recent advances made by the speaker and his collaborators will be presented. Generation of large-scale magnetic field by...

Numerical simulation of wave propagation from deep waters to very shallow waters, including changes over real bottoms

2018-02-21

Speaker: José Simão Antunes do Carmo (Department of Civil Engineering, University of Coimbra)

See the attached file...

Application of data mining to structural biology

2018-02-07

Speaker: Irina S. Moreira (Center for Neuroscience and Cell Biology, Univ. Coimbra)

Contrary to the reductionist approach aimed at understanding individual components, the new data revolution allows the understanding of complicated interactions and pathways through the use of statistical Data Mining (DM). This is an active area of research in mathematic/computer science...

Time-analyticity of fluid particle trajectories in ideal fluid flow

2017-11-08

Speaker: Vladislav Zheligovsky (Russian Academy of Sciences)

In his 1815 manuscript, Cauchy showed that the equations governing the motion of particles in ideal fluid flow can be once integrated in time. This yields what is now known as the Cauchy invariants. The invariants are then used to derive recurrence relations for the time-Taylor coefficients...

Oscillatory and nonoscillatory behavior of a differential delay system of order n

2017-10-11

Speaker: Sandra Pinelas (Academia Militar)

See file attached...

Early exercise boundaries for American-style knock-out options

2017-05-18

Speaker: José Carlos Dias (ISCTE-IUL Business School)

Under mild assumptions, this paper proposes a novel representation for the early exercise boundary of American-style double knock-out options in terms of the simpler optimal stopping boundary of a nested single barrier American-style contract. Therefore, and from now on, any single-factor...

The $\theta$-parareal schemes

2017-05-03

Speaker: Richard Tsai (Univ. of Texas at Austin, USA)

We propose a variant of the parareal method for parallel-in-time computation of time dependent problems. We call it the θ-parareal schemes because it formally resembles the θ-schemes for discretizing time dependent partial differential equations. We analyze the linear stability of...

Fast algorithms for high frequency wave propagation

2017-04-12

Speaker: Bjorn Engquist (Univ. of Texas at Austin, USA)

Direct numerical approximation of high frequency wave propagation typically requires a very large number of unknowns and is computationally very costly. We will discuss two aspects of this type of problem. One is the development and analysis of fast algorithms...

Volterra integral equations for non linear partial differential equations of integrable type

2017-04-07

Speaker: Luisa Fermo (Univ. of Cagliari, Italy)

Nonlinear partial differential equations (NPDE) of integrable type have important physical applications. They are used to describe electromagnetic waves in optical fibers, surface wave dynamics, charge density waves, breaking wave dynamics etc. Their corresponding initial value problem (IVP)...

Renormalized transport of inertial particles

2017-03-22

Speaker: Marco Martins Afonso (CMUP, Univ. Porto)

We study how an imposed fluid flow - laminar or turbulent - modifies the transport properties of inertial particles, namely their terminal velocity, effective diffusivity, and concentration following a point-source emission.Such quantities are investigated by means of analytical and...

Constrained partitions in graphs: bio and financial applications

2017-02-15

Speaker: Pedro Martins (IPCoimbra and CMAF-CIO)

This seminar addresses partition problems in graphs, from an applied perspective. We discuss results and formulations, ranging from very restrictive partition components (partition into cliques) to less restrictive ones (partition into trees - a forest). We also compare these results with...

Optimal simplex finite-element approximations of arbitrary order in curved domains circumventing the isoparametric technique

2017-02-10

Speaker: Vitoriano Ruas (Univ. Pierre et Marie Curie, Paris, and Catholic Univ., Rio de Janeiro)

One of the reasons for the undeniable success of the finite-element method in the applied sicences is its great versatility to deal with different types of geometries. This is particularly true of problems posed in curved domains of arbitrary shape. In this case method's isoparametric...

Systems of partial differential equations arising from population dynamics and neuroscience: Free boundary problems as a result of segregation

2016-12-14

Speaker: Verónica Quítalo (Univ. Coimbra - CoLab UT Austin Portugal Program)

In this talk we will present some two phase free boundary problems arising from population dynamics. We will focus on systems with fully nonlinear diffusion and local interaction, and linear systems with a (non local) long range interaction. In the long range model, the growth of a...

A short survey on Copositive and Completely Positive optimization

2016-12-07

Speaker:

Paula Amaral (Univ. Nova de Lisboa)

Copositive (Cop) and Completely Positive (ComP) Optimization is a recent and growing area of research. It has shown that several NP-hard optimization problems can be expressed as Cop or Comp programs, linear programs over the convex cone of copositive or completely positive matrices.In this...

The p-median on disconnected graphs

2016-11-09

Speaker: Jorge Orestes Cerdeira (Univ. Nova de Lisboa)

The <i>p</i>-median problem is a well-known NP-hard combinatorial optimization problem that seeks for the location of p facilities on the vertices (customers) of a graph G to minimize the sum of transportation costs for satisfying the demands of the customers from the...

Implementing a stable version of the tau method in a toolbox

2016-10-19

Speaker: José Matos (ISEP)

The Lanczos' tau method is a spectral method originally proposed to solve linear differential problems with polynomial coefficients. Generalizations to extending its domain of application to integro-differential, nonlinear and functional-differential problems, among others, have been made....

Finite difference methods for the reaction-wave-diffusion equation with distributed order in time

2016-06-01

Speaker: Magda Rebelo (CMA/UNL)

https://dl.dropboxusercontent.com/u/15380061/Abstract_MagdaRebelo.pdf...

Biology and Mathematics: a strategic alliance against cancer through new anti-tumoral therapies

2016-04-20

Speaker: Emanuela Signori (Univ. Rome, Italy)

Cancer remains one of the leading causes of death globally, affecting both sexes equally with an estimated 12.7 million cases around the world. This number is expected to increase to 21million by 2030, despite several curative strategies are offered to the patients. Therefore, new and...

Numerical investigations of spatially segregation models

2016-04-13

Speaker: Farid Bozorgnia (IST, Univ. Lisboa)

In this talk, we consider different models of Reaction-Diffusion system which describe the interactions between biological components. Thesemodels are:Adjacent segregation: The adjacent segregation model has been studied extensively [2]. In this model particles annihilate on contact, and...

On mixed and stabilized finite element methods for the obstacle problem

2016-02-12

Speaker: Juha Videman (IST, Univ. Lisboa)

The abstract is in the attached pdf file...

Computational modeling of hematopoietic stem/progenitor cells expansion and differentiation

2016-01-20

Speaker: Javad Hatami (Univ. Minho)

Quantifying the effect of exogenous parameters regulating hematopoietic stem/progenitor cells (HSC/HPC) expansion and differentiation will enhance to design robust and efficient protocols to be used for cell‐based therapies. Herein, a computational model was developed that...

Exponential splitting methods for the time integration of the Klein-Gordon equation with Hagstrom-Warburton high-order absorbing boundary conditions

2016-01-18

Speaker: Ana M. Portillo (Univ. Valladolid, Spain)

Klein-Gordon equations on an unbounded domain are considered in one dimensional and two dimensional cases. Numerical computation is reduced to a finite domain by using the Hagstrom-Warburton high-order absorbing boundary conditions. The space discretization is reached by means of finite...

From medical images to computational hemodynamics: a robust pipeline

2015-12-09

Speaker: Ana J. João (CEMAT-IST, ULisboa)

In the past decade, with the proliferation of technology and the increase of its capability, Computational Fluid Dynamics (CFD) has become a popular tool in several applications. This combined with our desire of increasing human life expectancy has lead to the combination of CFD and...

A numerical solution for a governing equation of Lévy motion

2015-11-04

Speaker: Ercília Sousa (CMUC, Univ. Coimbra)

This study looks at a governing equation of Lévy motion. This governing equation is a generalization of the classical, deterministic advection diffusion equation, just as Lévy motion is a generalization of Brownian motion. It can be represented by fractional derivatives, which...

A coupled release-absorption model for drug delivery systems

2015-10-07

Speaker:

Giuseppe Pontrelli (Istitupo per le Applicazioni del Calcolo, Rome, Italy)

In this talk I will present a mathematical model describing the release from a drug delivery system, such as a coronary eluting stent or a transdermal patch.The problem is reduced to a dynamics of a two-phase substance between two coupled media of different properties and extents. The...

Object detection, multispectral fusion, motion analysis and tracking in aerial imagery and video

2015-07-08

Speaker: Kannappan Palaniappan (Univ. Missouri, Columbia, USA)

Visual feature-based tracking systems need to adapt to variations in the appearance of an object and in the scene for robust performance to avoid drift. Tracking in aerial imagery is challenging as viewing geometry, calibration inaccuracies, complex flight paths and back- ground changes...

Filtering, fusion, detection and segmentation of microvasculature vessel fluorescence imagery

2015-07-07

Speaker: Kannappan Palaniappan (Univ. Missouri, Columbia, USA)

Automatic segmentation of three-dimensional microvascular structures is needed for quantifying morphological changes and remodeling of blood vessels during development, disease and treatment processes. We use an approach for vessel segmentation that combines multiple single focus images use...

On computing efficient pairs of disjoint paths

2015-07-01

Speaker: Marta Pascoal (INESC / Univ. Coimbra)

Pairs of disjoint paths between two nodes in a network provide a primary path as well as a backup path, such that the latter can be used in case one of the arcs of the first is not available. The problem of finding the shortest pair of disjoint paths can be formulated as a minimum cost flow...

Modeling Dengue disease: two real outbreaks - theoretical and practical issues

2015-06-17

Speaker: Maria Teresa Monteiro (ALGORITMI, Univ. Minho)

Epidemiology has become an important issue for modern society. Demographic evolution, accelerated urbanization, increased traveling and climate change, all favor the propagation of infectious diseases.Dengue is the most rapidly spreading mosquito-borne viral disease in the world. According...

Quaternion Newton-like methods

2015-06-03

Speaker: Maria Irene Falcão (Univ. Minho)

It is a well known fact that the algebraic as well as the geometric properties of complex holomorphic functions are not the same for their generalizations in quaternion analysis. In particular, because of the non-commutativity of quaternion multiplication, the use of root-finding methods...

Wavelets in Economics and Political Science

2015-05-06

Speaker: Maria Joana Soares (Univ. Minho)

The use of wavelet analysis is already very common in a large variety of disciplines, such as physics, geophysics, signal and image processing, medicine, biology, etc. More recently, wavelet tools have also been applied successfully in the areas of economics and finance. In spite of their...

Harmonic Analysis for the Natural Sciences

2015-04-22

Speaker: Luís Daniel Abreu (ARI-Austrian Academy of Sciences)

In the Natural Sciences, researchers are often faced with three problems of significant mathematical complexity. The first problem arises in every science where the observation process plays an important role: the need of restricting their measurements to a subregion of the ambient...

Computational hydrodynamics, from theory to practice

2015-04-15

Speaker: José S. Antunes do Carmo (Marine and Environmental Sciences Centre/UC)

In the 80’s, numerical models based on the Saint-Venant equations, or shallow water equations, were frequently used in practical applications. However, as has been widely demonstrated, in shallow water conditions and for some types of waves, models based on a non-dispersive theory, of...

Assessment of image derived PET quantification techniques

2015-04-08

Speaker: Miguel Patrício (Lab. Biostatistics and Medical Informatics, IBILI-FMUC)

Data detected by a positron emission tomography (PET) scanner is translated into concentration of radiotracer by using image reconstruction methods. Applying reconstruction algorithms will only retrieve the radiotracer concentration. However, there will be no discrimination between...

Modeling blood flow and mass transport by a drug eluting stent

2015-03-18

Speaker: Elias Gudiño (IST, Lisboa)

In this seminar we will present a fully coupled model for the description of blood flow and mass transport by a drug eluting stent in blood vessels. In order to obtain a numerical solution of the problem, we use an iterative splitting scheme over a stabilized finite element method together...

Some recent mathematical ideas for applications in biology

2015-02-11

Speaker: Ezio Venturino (Univ. Torino, Italy)

In this talk classical models in ecology and epidemiology will be presented and reviewed. These two fields have grown independently for a long time. Scientists have treated them separately, but only fairly recently have begun to realize that they do influence one another profoundly. Some...

Numerical modeling of complex fluid flows using the Finite Volume Method

2014-12-10

Speaker: Luís Ferrás (Inst. Polímeros e Compósitos, Univ. do Minho)

In this work we present a study on flows of Newtonian and Non-Newtonian fluids, carried out both analytically and numerically. Industrial applications of these flows are found in classical industries such as in polymer processing (for instance in extrusion) and in more modern applications as...

Constrained optimization techniques for quadratic matrix model updating

2014-11-12

Speaker:

Marcos Raydan (Univ. Simón Bolívar, Venezuela)

The Quadratic Finite Element Model Updating Problem (QFEMUP) concerns with updating a symmetric second-order finite element model so that it remains symmetric and the updated model reproduces a given set of desired eigenvalues and eigenvectors by replacing the corresponding ones from...

The MOOD method, principle and (some) examples

2014-10-15

Speaker: Stéphane Clain (Univ. Minho)

We present a new finite volume method to provide 6th-order approximations for hyperbolic problems.The technique is based on the one hand to a conservative polynomial reconstruction which enableto provide local accurate representations and an a posteriori limitation to prevent from...

Computational methods in the fractional calculus of variations

2014-10-01

Speaker: Delfim F. M. Torres (Univ. Aveiro)

The fractional calculus of variations and fractional optimal control are generalizations of the corresponding classical theories, allowing problem modeling and formulations with arbitrary order derivatives and integrals. Because of the lack of analytic methods to solve such fractional...

On approximation by periodic splines: theory and application

2014-09-24

Speaker: Rolf D. Grigorieff (Technische Univ. Berlin, Germany)

The talk is concerned with the existence of multiple knot periodic splines satisfying general Hermite interpolation conditions and their approximation power in Sobolev spaces. The key for such results are necessary and sufficient conditions for the existence of interpolating cardinal splines...

Optimal basis algorithm and its application to matrix scaling

2014-07-25

Speaker: Oleg Burdakov (Linköping Univ., Sweden)

We present the optimal basis (OB) problem and the OB algorithm that we proposed in BIT (1997) {\bf 37}, 591-599. The OB problem is formulated as follows. Given $m+1$ points $\{x_i\}^{m}_{0}$ in $R^n$ which generate an $m$-dimensional linear manifold, construct for this manifold a maximally...

Non-Fickian models for biodegradable drug eluting stents

2014-07-09

Speaker: Jahed Naghipoor (CMUC)

In recent years, mathematical modeling of cardiovascular drug delivery systems has become an effective tool to gain deeper insights in the cardiovascular diseases like atherosclerosis. In the case of coronary biodegradable stent which is a tiny expandable metallic mesh tube covered by...

Explicit Leap-frog DG method for time domain electromagnetic wave propagation

2014-06-04

Speaker: Maryam Khaksar Ghalati (CMUC, Univ. Coimbra)

The discontinuous Galerkin time domain methods are now popular and efficient way for the solution of wave propagation problems. The motivation of modeling scattered electromagnetic wave propagation through the human eye’s structure brings us to solving aMaxwell’s equations with...

Nonlinear propagation of waves of short wavelength in dispersive systems

2014-05-28

Speaker: Sílvio Gama (Univ. Porto)

We discuss the nonlinear propagation of waves of short wavelength in dispersive systems and we present the simplest nonlinear short-wave dynamics: $u_{tx} = u - 3 u^2$. We present an algorithm to integrate numerically this equation for periodic and non-periodic boundary conditions. We also...

Nonlocal models for image processing: properties and applications

2014-05-23

Speaker: Eduardo Cuesta (Univ. Valladolid, Spain)

One of the alternatives for the mathematical formulation of image processing problems is based on local, nonlinear PDEs models. In the first part of the talk, a brief overview of them, with special regards to morphological and structural properties, will be done. In the second part, some...

On the numerical approximation of algebraic equations with symmetries

2014-05-21

Speaker: Angel Durán (Univ. Valladolid, Spain)

The resolution of systems of algebraic equations with symmetry groups appears in the mathematical treatment of many models, [1, 2]. These groups consist of transformations that map solutions of the algebraic system into other solutions. Some consequences of the existence of such symmetry...

GLODS: Global and Local Optimization using Direct Search

2014-02-05

Speaker:

Ana Luísa Custodio (Univ. Nova de Lisboa, Portugal)

Locating and identifying points as global minimizers is, in general, a hard and time-consuming task. Difficulties increase when the derivatives of the functions defining the problem are not available for use. In this talk, we propose a new class of methods suited for global derivative-free...

Numerical solution of Sturm--Liouville problems via Fer streamers

2014-01-08

Speaker: Alberto Gil C. P. Ramos (Univ. Cambridge, UK)

We address the numerical challenge of solving Sturm-Liouville problems in Liouville's normal form, with regular boundary conditions and a continuous and piecewise analytic potential. The novelty of our approach, which is based on a non-standard truncation of Fer expansions, which we call...

Mathematical modelling of Angiogenesis -flow, elasticity and experiments

2013-11-20

Speaker: Rui Travasso (Center for Computational Physics, Univ. Coimbra)

Understanding angiogenesis in a pathological setting is a challenging problem with important consequences for diagnosis and treatment of severe diseases such as cancer. We present a multi-scale phase-field model that combines the benefits of continuum physics description and the capability...

Optimal control applications in blood flow simulations

2013-10-30

Speaker: Jorge Tiago (IST, Lisboa)

Blood flow simulations can be improved by integrating known data into the numerical simulations. Data assimilation techniques based on a variational approach can have an important role on this. We will introduce a nonlinear optimal control problem to reconstruct a blood flow profile from...

Some recent developments of a non-dissipative DGTD method for time-domain electromagnetics

2013-10-29

Speaker: Stéfane Lanteri (INRIA Sophia Antipolis-Méditerranée)

Nowadays, a variety of modeling strategies exist for the computer simulation of electromagnetic wave propagation in the time domain. Despite a lot of advances on numerical methods able to deal accurately and in a flexible way with complex geometries through the use of...

Experimental Optimization: the elephant in the room

2013-10-09

Speaker: Bunin Gene (EPFL, Lausanne, Switzerland)

Experimental optimization problems, though ubiquitous in the applied sciences, are a surprisingly underdeveloped field from the theoretical perspective. In this talk, we will define a canonical experimental optimization form, show how it is a generalization of the better-known...

Hermite finite elements for fluid flow and heat transfer

2013-10-02

Speaker: Vitoriano Ruas (UPCM-Paris 6, France)

Traditionally Hermite finite elements have been used to solve fourth or higher order boundary value PDE's, for in this case minimum continuity of solution derivatives must be ensured. It turns out that nothing prevents this kind of methods from being used to solve second order boundary value...

On error control and adaptivity for convection-dominated problems

2013-09-25

Speaker: Emmanuil H. Georgoulis (Univ. Leicester, UK)

Advection-dominated advection-diffusion-reaction elliptic and parabolic problems are known to be challenging numerically, due to the stiffness created by the interplay between the advection and the diffusion. In the context of ﬁnite element methods, a number of techniques which...

Cliques and cut-cliques: formulations and applications

2013-07-10

Speaker: Pedro Coimbra (ISCAC, Polytechnic Institute of Coimbra)

A network/graph provides an abstract representation, establishing the relationships among a set of elements. It helps organizing the information and provides an overall view of the underlying system.These structures are being used in a large number of areas and scientific domains, namely in...

A new look to non-Fickian diffusion

2013-06-12

Speaker: Elias Gudiño (Univ. Coimbra)

In this talk a non-linear mathematical model to describe absorption phenomena in polymers is proposed. The model is established assuming that the diffusing penetrant causes a deformation which induces a stress driven diffusion and consequently a non-Fickian mass flux. We also present a...

Eigenvalue complementarity problem: applications and algorithms

2013-02-20

Speaker: Luís Merca Fernandes (IP Tomar/IT)

The Eigenvalue Complementarity Problem (EiCP) finds important applications in different areas of science and engineering and differs from the traditional Eigenvalue Problem on the existence of nonnegative constraints on its variables and complementarity constraints between pairs of...

On multi-objective sequence alignment: formulation and algorithms

2012-12-19

Speaker:

Maryam Abbasi (DEI, Univ. Coimbra)

Sequence alignment is used to identify regions of similarity that may indicate functional, structural and/or evolutionary relationships between two or more biological sequences. Usually, the quality of an alignment is given by a score function that is a weighted sum of several components,...

Modeling non-Fickian diffusion processes

2012-12-12

Speaker: Elias Gudiño (CMUC)

An important problem in controlled release technology is the diffusion of a penetrant into a polymeric carrier where a drug is dispersed. A suitable choice for simulating drug delivery can be the classical Fick’s law. However to model the sorption of the liquid agent an equation that...

Multiscale analysis in hydrodynamics

2012-11-28

Speaker:

Sílvio Gama (Univ. Porto)

This seminar will start with a brief introduction to multiscale techniques. Afterwards, we will use these techniques to derive the large scale transport coefficients (eddy viscosity tensor included), as well as the equations that govern the large-scale dynamics. Time permitting, some results...

Mathematical models for the simulation of organic optoelectronic devices

2012-10-31

Speaker: Luís Morgado (Univ. Trás-os-Montes e Alto Douro)

Organic semiconductors, and in particular the polymeric, are of enormous interest for high-volume and low-cost manufacturing electronics industry, generally referred to as “printed electronics”. Considering that the first organic light-emitting device (OLED) based on low...

A non-polynomial collocation method for fractional differential equations

2012-10-31

Speaker: Maria Luísa Morgado (Univ. Trás-os-Montes e Alto Douro)

In this work we are concerned with the numerical approximation of fractional differential equations. We will focus on initial and terminal value problems for ordinary differential equations of non-integer order. The approach used is based on the equivalence between this kind of...

Matrix operations of almost linear complexity for computing eigenpairs of large dimensional problems

2012-10-24

Speaker: Paulo Vasconcelos (CMUP)

We consider the numerical solution of a large eigenvalue problem resulting from a nite rank discretization of an integral operator. We are interested in computing a few eigenpairs, with an iterative method, so a matrix representation that allows for fast matrix-vector products is required....

Smoothing and worst-case complexity for direct-search methods in nonsmooth optimization

2012-10-10

Speaker: Nima Garmanjani (Univ. Coimbra)

For smooth objective functions it has been shown that the worst-case cost of direct-search methods is of the same order as the one of steepest descent. Motivated by the lack of such a result in the nonsmooth case, we propose, analyze, and test a class of smoothing...

A derivative-free optimization algorithm with subspace technique

2012-10-03

Speaker: Zaikun Zhang (Univ. Coimbra)

We will talk about optimization algorithms that do not use derivatives, namely, derivative-free algorithms. We discuss how to incorporate subspace techniques into this type of algorithms, and present a new derivative-free algorithm with subspace techniques. For the new algorithm,...

Presentation of differential-algebraic systems with delays (DAD) and applications of fractional derivatives to DAD systems

2012-09-26

Speaker: Zbigniew Zaczkiewicz (Politechnika Bialostocka, Poland)

TBA...

FEM solutions of some Boussinesq-type models for surface water waves

2012-07-11

Speaker: Nuno Lopes (CMAF, Univ. Lisboa)

A class of improved Boussinesq-type models to simulate the propagation and generation of nonlinear dispersive waves is presented. The models are derived in order to keep some dispersive characteristics of higher-order ones. Some stability properties of the numerical models are discussed....

Strong discontinuities in the scope of the discrete crack approach

2012-05-23

Speaker: Daniel Dias da Costa (Univ. Coimbra)

The use of the discrete crack approach and Nonlinear Fracture Mechanics opened the possibility of accurately modelling fracture behaviour of quasi-brittle materials, such as concrete, mortar and masonry. In this approach, it is assumed that microcracking localises into a surface of...

An agency for Mathematics in interaction with enterprises and society in France

2012-04-26

Speaker: Christophe Prud'homme (Univ. Grenoble, France)

I will discuss the creation and the first year of existence of the french Agency for Mathematics in Interaction with Enterprises and Society (AMIES) [1]. First I start with the context in which the agency was funded then I present the organisation, its objectives and the tools it provides to...

Network Optimisation with non-deterministic arc parameters: an application to bloodstream object location

2012-03-07

Speaker: Deolinda M. L. D. Rasteiro (ISEC)

Abstract: In this talk we propose algorithms which determine the path that minimizes the expected value of a utility function over a dynamic probabilistic network with discrete or continuous real random variables (parameters) associated to each emerging arc. To obtain the optimal dynamic...

Models and algorithms for network design problems

2012-01-26

Speaker: Michael Poss (Univ. Libre de Bruxelles, Belgium)

In this talk, we will have a rapid look at diverse problems arising in the context of network design. We start with a brief introduction to enumeration techniques used in integer programming. Then, we present different problems occurring in telecommunications and electrical power systems. We...

Non-smooth analysis and optimization

2011-10-20

Speaker: Suvendu Ranjan Pattanaik (DMUC)

In this talk, we show that for a large class of optimization problems, the Lagrange multiplier rule can be derived from the so-called approximate multiplier rule and we prescribed an approximate gradient multiplier rule in handling non-smooth problems. Also in this talk we will cover some of...

Lifts of convex sets

2011-09-21

Speaker: João Gouveia (Mat FCTUC)

It is well-known that some complicated polytopes can be represented as projections of much simpler polytopes permitting polynomial time algorithms for linear optimization over them. In 1991 Yannakakism established a connection between the existence of such lifts and the nonnegative rank of...

Multi-criterion optimization of a public transport network

2011-05-27

Speaker: Carlos Caçador (Novabase)

The shortest path problem is a well-known and widely studied problem of operational research. Although used in several areas, is in the area of...

Two problems combining routing and location

2011-05-20

Speaker: Marta Pascoal (DMUC)

In this talk we describe two problems that combine the determination of a route between two given nodes in a network and the location of a set of special nodes along the route, the minimum cost path problem with relays and the pipeline and valve location problem. It is shown that rather than...

In vitro drug dissolution profiles: comparison and mathematical modeling

2011-05-06

Speaker: Carla M. Lopes (Univ. Fernando Pessoa)

...

Evaluating the Fréchet derivative of the matrix pth root

2011-04-29

Speaker: João Cardoso (ISEC)

It is well-known that the sensitivity of the matrix pth root (and primary matrix functions in general) to small perturbations in the data is measured by a condition number based on the norm of the Fréchet derivative. In this talk we show that computing the Fréchet derivative of...

Direct search methods: robustness and efficiency in derivative-free optimization

2011-01-05

Speaker: Ana Luísa Custódio

In this talk we will focus on the numerical optimization of extended-value, nonsmooth functions, without using derivatives. We will start by reviewing the class of directional Direct Search Methods, paying particular attention to the situation where the objective function is...

Numerical schemes for short wave long wave interaction equations

2010-12-15

Speaker: Paulo Amorim (CMAF/Univ. Lisboa)

We prove convergence of some finite volume type numerical schemes for short wave long wave interaction equations. These are systems of coupled nonlinear PDEs consisting of a Schroedinger equation for the short waves and a hyperbolic conservation law modeling the long waves. We present some...

Schwarz waveform relaxation algorithms for some semilinear reaction-advection-diffusion type equations

2010-10-27

Speaker: Filipa Caetano (Univ. Paris-Sud 11, France)

We are interested in domain decomposition algorithms of Schwarz waveform relaxation type to compute approximate solutions of some nonlinear evolution equations. Schwarz waveform relaxation algorithms are based on a decomposition of the problem in space, like classical Schwarz methods,...

Exploration of genomewide data: future challenges and the state of the art

2010-10-06

Speaker: Magnus Fontes (Lund University, Sweden)

I will present a collection of statistical and mathematical methods useful for the exploration of some types of multivariate data and in practice show how we have implemented them in the commercial software Qlucore Omics Explorer (QOE). In particular I will discuss classical principal...

The proposal of a bone remodeling model based on generalized thermodynamics potentials

2010-09-22

Speaker: Emílio Graciliano Ferreira Mercuri (Univ. Porto / Univ. Fed. Paraná, Brasil)

The bones are the elements responsible to support the body and one of their main characteristics is the capability of self adaptation, which consists in continuous changes in their microstructure during life-time. The process responsible for this modification is called internal remodeling...

Numerical methods that preserve the fixed points of a differential equation

2010-07-14

Speaker: Higinio Ramos (Departamento de Matemática Aplicada, Univ. Salamanca, Espanha)

--...

Ergodic transitions in continuous-time random walks

2010-06-30

Speaker: Roberto Venegeroles (Centro de Matemática, Computação e Cognição - UFABC - Brazil)

Abstract: We consider continuous-time random walk models described by arbitrary sojourn time probability density functions. We find a general expression for the distribution of time-averaged observables for such systems, generalizing some recent results presented in the literature. For...

Highly accurate computation of eigenvalues of tridiagonal matrices

2010-05-19

Speaker: Rui Ralha (U. Minho)

We present a method to improve or just guarantee the accuracy of the approximations delivered by any fast method for the eigenvalues of symmetric tridiagonal matrices.The motivation for this approach is two-folded: 1) the fastest state-of-the-art routines in LAPACK do not always deliver...

Mesoscale cracking of composites

2010-05-05

Speaker:

Miguel Patrício (CMUC and Instituto Politécnico de Leiria)

The usage of composites in high performance products such as aerospace components, storage tanks or racing car bodies is increasing. Typically, a lightweight yet strong material is sought, capable of withstanding harsh loading conditions. Such conditions are prone to the occurrence of...

On the detection of an immersed rigid body

2010-04-07

Speaker:

Ana Leonor Silvestre (IST, Lisboa)

TBA...

Numerical methods for Volterra integral equations with weakly singular kernel

2010-03-24

Speaker: Teresa Diogo (CEMAT/Instituto Superior Técnico, Lisboa)

This talk is concerned with the numerical solution of a Volterra integral equation with non-standard weakly singular kernel which may arise in connection with some heat transfer problems. The singular behaviour of the solution near the origin causes the loss of the optimal (global)...

Mixed-type functional differential equations: analysis and computational methods

2010-03-03

Speaker: Pedro Lima (Instituto Superior Técnico, UTL)

Abstract in attachment ...

Inverse scattering problems and medical imaging

2010-02-04

Speaker: Pedro Serranho (IBILI, Coimbra)

Inverse Scattering Problems have a wide range of applications, as radar and sonar, seismology and medical imaging. In this talk we intend to present a brief discussion on some particular inverse scattering problems, focusing on their mathematical formulation and...

Complexity of Interior-point methods for solving convex conic feasibility problems with finite precision

2009-11-05

Speaker: Vera Roshchina (University of Évora)

Polynomial complexity of interior-point methods (IPMs), as well as their practical efficiency have made them the methods of choice for solving a vast number of optimization problems. The first polynomial-time IPM was introduced by Karmarkar for Linear Programming, and later Nesterov and...

Rheological and multiscale FSI models for the numerical simulation of blood flow

2009-10-14

Speaker: Alexandra Moura (IST, Lisboa)

The mathematical modelling and numerical simulation of the cardiovascular system is a very challenging task, due to its geometrical and functional complexity. Namely, in this lecture we address three main difficulties in this field. In particular, blood is a non-Newtonian shear-thinning...

From medical imaging to clinical CFD

2009-10-01

Speaker: Alberto Gambaruto (IST, Lisbon)

The talk will outline steps of how to obtain a virtual model from medical images, that can be used for numerical simulations. Steps of image enhancement, segmentation and interpolation, geometric modelling, mesh optimisation and surface smoothing are outlined. Numerical simulations for...

A reduced basis multiscale method

2009-07-09

Speaker: Christophe Prud'homme (Université de Grenoble, France)

We are interested in the two following model problems:The first equation is a diffusion equation with variable coefficients which models many problems such as the prediction of the presence of oil or gaz in porous media. u is then the pressure of the fluid and represents the permeability of...

Interior point methods for complementarity problems

2009-06-25

Speaker: Florian Potra (University of Maryland Baltimore County, USA)

Complementarity is ubiquitous in the natural and social sciences. It is a fundamental principle underlying equilibrium. In a primal-dual description of a system it means that either the primal or the corresponding dual component of the solution vector must vanish. There are many problems...

Decomposition-based optimization in engineering design

2009-06-05

Speaker: Michael Kokkolaras (University of Michigan, USA)

In many industry branches, including automotive and aerospace, optimal system design problems appear in a decomposed form: design optimization tasks, associated with the elements that comprise the system, are distributed among departments or outsourced to suppliers. Smooth system integration...

Parameter driven multi-state duration models: simulated vs. approximate maximum likelihood estimation

2009-06-04

Speaker: André A. Monteiro (Tinbergen Institute, The Netherlands)

Likelihood-based inference for the Multi-state Latent Factor Intensity Model is hindered by the fact that exact closed-form expressions for the implied data density are not available. This is a common and well-known problem for most parameter driven dynamic Econometric models. The estimation...

Recent progress in the application of semidefinite programming to discrete optimization

2009-05-21

Speaker: Miguel Anjos (University of Waterloo, Canada)

The max-cut algorithm of Goemans and Williamson is 15 years old in 2009, and its impact in the area of semidefinite programming has been remarkable. In this talk, I will survey some of the main modelling and algorithmic developments since 1994 in the application of semidefinite programming...

Solving semi-infinite programming problems by reduction method

2009-05-14

Speaker: Ana Pereira (Instituto Politécnico de Bragança)

It will be presented a review of reduction type methods to solve nonlinear semi-infinite programming problems. In the last years a large type of techniques were presented in literature to solve SIP problems based on reduction method. These reduction type methods are based on merit functions...

Optimization of posynomials under l^p constraints

2009-02-12

Speaker: Immanuel M. Bomze (University of Vienna)

We will consider the problem to maximize a positive linear combination of monomials involving (possibly fractional or irrational) positive powers of n variables over the intersection of the l^p sphere with the positive orthant. After recapitulating seminal works from the 1960s until...

Construction of a High Order Fluid-Structure Interaction Solver

2009-02-05

Speaker: Gonçalo Pena (CMUC)

Accuracy is critical if we are to trust simulation predictions. In settings such as fluid-structure interaction it is all the more important to obtain reliable results to understand, for example, the impact of pathologies on blood flows in the cardiovascular system. In this paper,...

Analysis of a fully coupled geomechanics and reservoir flow model with stress-dependent permeability

2008-12-18

Speaker: Sílvia Barbeiro (CMUC)

The modeling of coupled mechanics and flow in porous media attracts researchers from different areas and is of great importance in a diverse range of engineering fields. Land subsidence, due to consolidation or compaction, which is often caused by exploitation of subsurface...

A recursive multi-level trust-region algorithm for bound constrained optimization

2008-12-11

Speaker: Serge Gratton (CNES-CERFACS)

We consider the solution of large scale optimization problems, subject to bound constaints, arising in the discretization of infinite dimensional problems. In particular, we suppose that we have access to a collection of functions representing the problem for different value of a...

Computational methods for forward-backward differential equations

2008-11-20

Speaker: Filomena Teodoro (Instituto Politécnico de Setúbal)

This seminar is concerned with the approximate solution of forward-backward differential equations of the general form x'(t)=α(t)x(t)+β(t)x(t-1)+γ(t)x(t+1). We search for a solution x, defined for t∈[-1,k], (k∈N), which takes given values on the intervals [-1,0]...

Fractional Calculus: Application in Modeling and Control

2008-11-13

Speaker: J. A. Tenreiro Machado (ISEP)

In 1695 L'HÎpital wrote a letter to Leibniz asking for the meaning of Dny for n = 1/2. Leibniz replied 'It seems that useful consequences shall be drawn from these paradoxes one day, as there are no paradoxes that do not prove useful'. The term 'Fractional Calculus' (FC) was adopted at that...

Optimization methods for sparse covariance selection for Gaussian models

2008-10-30

Speaker: Katya Scheinberg (Math. Sciences, IBM Research)

Recently proposed $l_1$-regularized maximum-likelihood optimization methods for learning sparse Markov networks result into convex problems that can be solved optimally and efficiently. However, the accuracy of such methods can be very sensitive to the choice of the regularization...

Parallel Perfomance Prediction for Multilevel Numerical Software

2008-10-16

Speaker: Giuseppe Romanazzi (CMUC)

We propose a model for describing and predicting the performance of parallel numerical multilevel software on distributed memory architectures within a multi-cluster environment. The goal of the model is to allow reliable predictions to be made as to the execution time of a given code on...

Using dual techniques to derive condition numbers. Application to componentwise and mixed condition numbers for linear least squares.

2008-09-18

Speaker: Marc Baboulin (CMUC)

We prove duality results for adjoint operators and product norms in the framework of Euclidean spaces. We show how these results can be used to derive condition numbers especially when perturbations on data are measured componentwise relatively to the original data. We apply this...

Flocks and Formations

2008-07-14

Speaker: J.J.P. Veerman (Department of Mathematics & Statistics, Portland State University)

Given a large number (the "flock") of moving physical objects (birds, robots, or otherwise), we investigate physically reasonable mechanisms of influencing their orbits in such a way that they move along a prescribed course and in a prescribed and fixed configuration (or "in formation")....

Some issues in dense linear algebra algorithms for multicore

2008-05-15

Speaker: Marc Baboulin (CMUC)

The advent of multicore processors will considerably influence future research in High Performance Computing. To take advantage of these architectures in dense linear algebra operations, new algorithms are proposed that use finer granularity and minimize synchronization points. After...

A multiresolution space-time adaptive scheme for the bidomain model in electrocardiology

2008-05-08

Speaker: Ricardo Ruiz Baier (Universidad de Concepción, Chile)

In this seminar we present a finite volume method enriched with a fully adaptive multiresolution scheme, a Runge-Kutta-Fehlberg adaptive scheme, and a locally varying time stepping, for solving the widely known monodomain and bidomain equations modeling the electrical activity of...

Global properties of epidemiological models and virus dynamics models with nonlinear incidence rates by Lyapunov direct method

2008-04-24

Speaker: Andrei Korobeinikov (University of Limerick)

Classical models of infectious diseases postulate that the spread of an infection occurs according to the principle of mass action and associated with that an incidence rate which is bilinear with respect to the interacting populations (the numbers of susceptible and infective individuals...

Uma nova técnica de rotulação para o problema do trajecto mais curto multi-objectivo

2008-02-28

Speaker: José Luís Esteves dos Santos

O problema do trajecto mais curto multi-objectivo (PTMCM) é definido numa rede em que vários critérios são atribuídos a cada arco. Em geral, existe conflito entre os vários objectivos pelo que a resolução do PTMCM consiste na determinação dos trajectos não-dominados (ND), isto é,...

Aplicações da optimização de forma na mecânica estrutural

2007-12-06

Speaker: Anca-Maria Toader (Universidade de Lisboa)

Area(s): ...

Uma introdução à optimização de forma

2007-11-29

Speaker: Cristian Barbarosie (Universidade de Lisboa)

Area(s): ...

Non-Fickian delay reaction-diffusion equations

2007-11-22

Speaker: José Augusto Ferreira (CMUC, Departamento de Matemática, Universidade de Coimbra)

The Fisher's equation is established combining the Fick's law for the flux with the mass conservation law. Assuming that the reaction term depends on the solution at some past time, delay Fisher's equation is defined. Integro-differential equations of Volterra type were introduced in the...

Mathematical models in hemorheology: an application.

2007-11-15

Speaker: João Janela (ISEG)

In this talk we describe the rheological properties of blood and discuss the main mathematical models used to describe blood flow. As an example of the use of non Newtonian models in blood flow, we show numerical results for a constrained optimization problem arising in the simulation of...

Very large least-squares for parameter estimation: algorithms and application

2007-11-08

Speaker: Marc Baboulin (CERFACS, França)

One of the main challenging task in parameter estimation is to be able to compute in a reasonable time a very accurate solution by considering a huge number of observations. We present a parallel implementation of an incremental least squares solver based on orthogonal transformations that...

Shape Optimal Design of Periodic Microstructural Materials

2007-11-05

Speaker: Svetozara I. Petrova (Institute of Mathematics, University of Augsburg, Germany)

We are concerned with shape optimal design of composite materials with periodic microstructures. The homogenization approach is applied to obtain the computationally feasible macromodel. The microstructural geometrical details of the microcells (such as lengths and widths of the different...

Integro-differential model of percutaneous drug absortion

2007-10-25

Speaker: Sílvia Barbeiro (CMUC, Departamento de Matemática, Universidade de Coimbra)

In this talk we propose a model for percutaneous absorption of a drug which consists in integro-differential equations with appropriate initial and boundary conditions. We study the qualitative properties of the model and its numerical approximation. Simulation of described numerical...

Recent Advances in Iterative Algorithms for Linear Inverse Problems under Non-quadratic Regularization

2007-06-19

Speaker: Mário A. T. Figueiredo, Instituto de Telecomunicações Instituto Superior Técnico Lisboa, Portugal

Iterative shrinkage/thresholding (IST) algorithms have been recently proposed to handle a class of convex (maybe non-smooth) unconstrained optimization problems arising in image restoration and other linear inverse problems (e.g., total-variation-based or wavelet-based restoration). It...

Análise de problemas discretos para um modelo de viscoelasticidade linear com memória

2007-05-10

Speaker: João Ricardo Branco (Instituto Superior de Engenharia de Coimbra)

Neste trabalho é estudada uma equação hiperbólica, com termo de memória temporal, que pode ser vista como uma perturbação singular da equação do calor com memória. São estudadas as propriedades qualitativas das soluções do problema com condições iniciais e de fronteira associadas às duas...

Modelos cinéticos de tipo BGK para gases quimicamente activos

2007-04-26

Speaker: Ana Jacinta Soares (Departamento de Matemáticada da Universidade do Minho)

A equação de Boltzmann (EB), proposta por Ludwig Boltzmann em 1872, constitui a parte analítica do modelo mais notável da teoria cinética dos gases que, a partir de uma abordagem de base estatística, descreve a evolução no espaço e no tempo de um gás inerte constituído por moléculas...

Generalized Newtonian fluid in a straight pipe using 1D models

2007-04-12

Speaker: Fernando Carapau (Univ. ??vora)

The aim of this talk is to analyze the axisymmetric unsteady flow of an incompressible generalized Newtonian fluid in a straight rigid and impermeable tube with circular cross-section of constant radius. To make this study, we use an approach based on the Cosserat theory (also...

Equidade e Eficiência na Optimização de Sistemas Multidimensionais de Erlang-B.

2007-01-26

Speaker: Jorge Sá Esteves (Dep. Matemática, Univ. de Aveiro)

Apresenta-se um problema de optimização convexa bicritério relativo à afectação de servidores entre grupos funcionais de Erlang-B (M/M/n/0), que ocorre na modelação de sistemas/redes de Teletráfego. A abordagem do problema de optimização é antecedida de um estudo numérico (propondo...

Novos Metodos MUSCL para os volumes finitos

2006-11-03

Speaker: Stéphane Clain (Laboratoire de Mathématique pour l'Ingeniérie et la Physique, Université de Toulouse III)

A tecnica MUSCL permite melhorar a precisao numerica do metodo dos volumes finitos. Em dimensao 2 ou 3, os algoritmos MUSCL classicos podem ser bastante complicados. Apresento uma nova tecnica de tipo MUSCL mais simples e eficaz. A ideia principal é considerar para cada interface um...

Equações de difusão-reacção com atraso: Propriedades qualitativas e quantitativas

2006-10-20

Speaker: Pascoal Silva (ISEC)

Modelos Matemáticos envolvendo equações de difusão-reacção com atraso substituem hoje, cada vez mais, modelos tradicionais de difusão-reacção. Nesta palestra apresentamos, para os modelos anteriores, resultados que caracterizam as propriedades qualitativas e quantitativas das soluções...

Qualocation with pseudodifferential operators using multiple knot periodic splines

2006-10-09

Speaker: R.D. Grigorieff (Technische Univ. Berlin)

The stability of discrete projections on multiple knot periodic splines on uniform meshes is studied. Results include their approximation power in Sobolev spaces, commutator and superapproximation properties. As an application the convergence of the qualocation method for elliptic periodic...

Segmenting Medical ImageS Using Level Sets

2006-07-17

Speaker: Donna Comissiong (CMUC)

Image segmentation is the process by which objects are separated from background information. Structural segmentation from two and three dimensional images is an important first step in the analysis of medical data obtained from MRI pictures. In this informal talk, we will outline efficient...

Complementary perspectives on optimization algorithms

2006-07-11

Speaker: J.L. Nazareth (Professor Emeritus, Washington State University, Affiliate Professor, University of Washington)

Simplex, interior-point, and memoryless quasi-Newton (QN) optimization algorithms are each viewed from two contrasting perspectives: the first facilitates computer implementation but runs counter to intuition, the second is both insightful and efficiency-revealing. For the memoryless QN...

Image Geometry in Non-Conventional Central Projection Cameras using Lifting of Coordinates

2006-06-07

Speaker: João Pedro Barreto (Dep. Engenharia Electrotécnica e de Computadores, FCTUC)

Central cameras are vision systems with a single effective viewpoint. In this cameras the light rays forming the image intersect in a single point in space called the projection center. Examples of central projection systems are the conventional perspective camera, cameras with radial...

Numerical aspects of the St Venant system for shallow water

2006-05-30

Speaker: Benoit Perthame
(??cole Normale Supérieure, Paris)

The shallow water description through the Saint-Venant system is usual for many applications (rivers flow, tidal waves, oceans). This is an hyperbolic system, relatively simple but that contains source terms describing the bottom topography and friction, and thus can undergo shock waves...

A convex quadratic characterization of the Lovász theta number

2006-05-24

Speaker: Carlos J. Luz (Escola Sup. Tecnologia de Setúbal / Instituto Politécnico de Setúbal)

A set of convex quadratic bounds on the stability number of a graph is introduced. A characterization of the famous Lovász theta number is established by proving that: a) This number is never worse than any of the above bounds and, b) It equals one of the above bounds. Further issues...

Connectivity in the design of protected area networks

2006-05-17

Speaker: Jorge Orestes Cerdeira
(Dep. Matemática, Inst. Sup. Agronomia)

A number of problems associated with the spatial structure in the design of networks of protected areas are not trivial, and solutions are not readily approximated intuitively. One such issue is that of identifying networks capturing the regional species assemblage, where some level of...

Block Mesh Refinement Algorithm for Simulations of Supersonic Turbulence

2006-03-22

Speaker: Miguel A. de Avillez [Department of Mathematics, University of Evora (Portugal) and Institut of Astronomy, University of Vienna (Austria)]

Turbulence in diffuse gases (e.g., interstellar gases) can have Reynolds numbers of the order of 107 or even larger. The source of such turbulence are point like explosions with energies of the order of 1051 erg that stir the medium continuously. Such turbulence decays on a time scale of the...

Improving Efficiency in Pattern Search Methods

2006-03-08

Speaker: Ana Luísa Custódio (FCT, UNL, CMUC)

Pattern search methods can be made more efficient if past function evaluations are appropriately reused. This class of methods is widely used in practice due to its simplicity and easy implementation, but the corresponding algorithms have the major drawback of sometimes using...

Principal Component Regression for Construction of Wing Weight Estimation Models

2006-02-08

Speaker: Humberto Rocha (Universidade Católica Portuguesa)

The multivariate data fitting problem occurs frequently in many branches of science and engineering. It is very easy to fit a data set exactly by a mathematical model no matter how the data points are distributed. But building a response by using a limited number of poorly distributed data...

Branch-and-price and multicommodity flows

2005-12-14

Speaker: Filipe Alvelos (Departamento de Produção e Sistemas, Universidade do Minho)

In this presentation, we discuss the application of column generation based algorithms to three multicommodity flow problems (MFP). In this type of problems, it is desired to route a set of commodities through a capacitated network at a minimum cost. In the linear MFP, each unit of each...

Quadratic Models for Portfolio Credit Risk with Shot-Noise Effects

2005-12-06

Speaker: Raquel M. Gaspar (Department of Finance, Stockholm School of Economics)

We propose a reduced form model for default that allows us to derive closed-form solutions to all the key ingredients in credit risk modeling: risk-free bond prices, defaultable bond prices (with and without stochastic recovery) and implied probabilities of survival. We show that all these...

A primal-dual method for TV-type image denoising

2005-11-09

Speaker: Georg Stadtler (CMUC)

Total-variation (TV) image reconstruction is well accepted for denoising images with sharp edges. The main advantage of the TV-approach, which was first proposed by Rudin, Osher and Fatemi in 1992, is that edges are not smeared in the reconstructed image. Mathematically, the problem is a...

Um método Newton-GMRES globalmente convergente com uma nova escolha para o termo forçante e algumas estratégias para melhorar o desempenho de GMRES(m)

2005-11-08

Speaker: Júlia Toledo Benavides (Departamento de Matemática Aplicada, Universidade Estadual de Campinas)

Neste trabalho, apresentamos um m?etodo de Newton inexato atrav?es da proposta de uma nova escolha para o termo for?cante. O m?etodo obtido ?e globalizado atrav?es de uma busca linear robusta e suas propriedades de converg??encia s??ao demonstradas. O passo de Newton inexato ?e obtido pela...

Friction and Contact Problems in Elasticity: Fenchel Duality, Infinite-Dimensional Semismooth Newton and Path-Following Methods

2005-10-25

Speaker: Georg Stadtler (CMUC)

In this talk, second-order methods for contact and friction problems in linear elasticity are developed and analyzed in infinite-dimensional function space. The main difficulty of these problems lies in the friction and contact conditions that are inherently nonlinear. We mainly consider...

A Stability Analysis of Polymerization Fronts

2005-09-21

Speaker: Donna M. G. Comissiong (Northwestern University, IL, USA, also a postdoc at CMUC)

Frontal Polymerization (FP) is a process of converting monomer into polymer via a localized zone that propagates through the monomer. It bears a strong resemblence to self-propagating high-temperature synthesis (SHS), which uses combustion waves to synthesize desired inorganic materials....

Duality Bounds in Global Optimization

2005-09-20

Speaker: Reiner Horst (University of Trier,Germany)

A survey is given of some astonishingly promising recent results in the use of (Lagrangian-)dual bounds in branch and bound methods for the global minimization of nonconvex functions over convex and nonconvex sets.In these methods,the calculation of good lower bounds is...

H-matrices and their characterization using iterative methods

2005-06-13

Speaker: Maria Alanelli (University of Crete)

In the theory of Numerical Linear Algebra the class of H-matrices is very important. In recent years many works have appeared that propose criteria for a complex nxn matrix A to be an H-matrix. In the present work , we propose one more such criterion together with an algorithm. Area(s): ...

Non-differentiable Optimization of Lagrangian Dual Formulations of Linear Programs with Recovery of Primal Solutions

2005-04-29

Speaker: Hanif D. Sherali (Virginia Tech, Department of Industrial and Systems Engineering)

We consider the solution of Lagrangian dual formulations of linear programs and examine various non-differentiable optimization techniques for obtaining both dual and primal solutions. The motivation for this study is that, for example, in the context of solving mixed-integer programs via...

Optimal Trees for Network Flow Problems: A Dynamic Programming Approach

2005-04-29

Speaker: Dalila M. Fontes (Faculdade de Economia da Universidade do Porto)

We consider the Single Source Uncapacitated (SSU) Minimum Cost Network Flow Problem (MCNFP) with general concave costs, in which a subset of arcs must be selected so that flow can be routed to vertices with known demands from a single source at minimum cost. A Dynamic Programming...

Um problema de partição multicritério de um território em zonas

2005-04-13

Speaker: José Figueira (Faculdade de Economia da Universidade de Coimbra) e Fernando Tavares Pereira (Departamento de Matemática da Universidade da Beira Interior)

Nesta comunicação iremos abordar alguns resultados relacionados com o problema da partição multicritério dum território em zonas. Cada zona é formada por um conjunto de átomos (unidades territoriais indivisíveis). Uma "partição" é formada por uma partição do conjunto de átomos em zonas...

Estimação da Função de Densidade de Probabilidade de Risco Neutro para Preços de Opções

2004-11-18

Speaker: Ana Margarida Monteiro (Faculdade de Economia da Universidade de Coimbra)

A atribuição de preços a opções é uma das áreas fundamentais da matemática financeira. O desenvolvimento da teoria dos preços das opções surge na sequência do trabalho de Black e Scholes, segundo o qual a variação do preço do activo subjacente a uma opção segue uma lei de probabilidade...

Modelo de Fluxo versus Modelo de Cobertura para um Problema de Reescalonamento de Enfermeiras

2004-11-04

Speaker: Margarida Vaz Pato (ISEG, Universidade Técnica de Lisboa)

O problema de reescalonamento de enfermeiras que temos vindo a estudar, responde a uma necessidade real das unidades hospitalares portuguesas de receberem apoio na tarefa de recomposição do plano de escalas do pessoal de enfermagem após comunicação de faltas ao serviço. Do ponto de vista...

Apresentação e análise do algoritmo da colocação dos docentes do concurso do ano lectivo de 2004/2005.

2004-11-03

Speaker: Luís Andrade (ATX Software)

Nesta palestra será apresentada de forma sumária a caracterização do problema da colocação dos docentes onde se distinguem dois aspectos: 1. A problemática relativa à mobilidade das candidaturas, isto é à transitividade dos destacamentos e a libertação e recuperação de vagas; 2. Os...

Levantamento de desigualdades válidas para modelos de programação inteira mista elementares.

2004-10-07

Speaker: Agostinho Agra (Universidade de Aveiro)

Será feito um breve resumo teórico dos principais resultados conhecidos relativos ao procedimento de levantamento de desigualdades válidas e à importância que assumem as funções superaditivas nesse procedimento. Considerando a descrição poliédrica do envolvente convexo de conjuntos...

Modelos para o problema da árvore de suporte com restrições de diâmetro ímpar

2004-09-30

Speaker: Cristina Agra (Universidade de Aveiro)

O problema da Árvore de Suporte de Custo Mínimo com restrições de Diâmetro (ASCM-D) consiste em determinar a árvore de suporte de menor custo tal que para cada par de nodos o único caminho que os une tem um limite máximo D (diâmetro) no seu comprimento. Este é um problema NP-difícil quando...

A Lagrange Newton Method with Inexact Jacobians for Large Scale Inequality Constrained Optimization

2004-07-20

Speaker: Moritz Diehl, Interdisciplinary Center for Scientific Computing, University of Heidelberg

We present a Lagrange Newton method for solution of large scale nonlinear programs with equality and inequality constraints. To avoid an expensive evaluation of the complete constraint Jacobian we propose a novel approach that does not need exact constraint Jacobians. The method uses...

Descrição poliédrica de conjuntos envolvendo duas variáveis inteiras

2004-07-08

Speaker: Agostinho Agra (Universidade de Aveiro)

Discutiremos o interesse do estudo de modelos de programação inteira mista (PIM) elementares como relaxação e/ou agregação de modelos mais gerais. Procederemos à descrição poliédrica do envolvente convexo de vários conjuntos de PIM envolvendo duas variáveis inteiras. Mostraremos que...

O problema do trajecto com custo de norma mínima

2004-03-18

Speaker: José Luís Esteves dos Santos (Departamento de Matemática, Universidade de Coimbra)

No problema do trajecto mais curto multi-objectivo (PTMCM) frequentemente nos deparamos com a determinação do "melhor" trajecto não dominado entre dois nós numa rede onde são considerados $k 1$ critérios diferentes para o custo dos arcos. A resolução do PTMCM implica a determinação de todos...

Modelos para problemas de árvores com restrições de salto e de diâmetro

2004-02-19

Speaker: Luis Gouveia (Universidade de Lisboa)

Para obter modelos fortes para cada um dos problemas propostos, é necessário ter uma boa representação do poliedro associado a um problema de determinação de 1 caminho com um numero máximo de arcos. Descrevem-se formulações estendidas para este subproblema. Em particular, apresenta-se uma...

Partição de torneios acíclicos de $k$ cores

2004-02-05

Speaker: Jorge Orestes Cerdeira (Instituto Superior de Agronomia, Univ. Técnica de Lisboa)

Seja $G_1$ um torneio acíclico com ordem topológica $0 Considere o grafo $G_2$ obtido tomando uma réplica de cada arco de $G_1$ e colorindo uma cópia de azul e outra de vermelho. Uma 2-partição de $N$ é um par de caminhos, um azul e outro vermelho, ambos de $0$ a $n+1$, em que cada...

Análise e simulação numérica de modelos de hemorreologia

2004-01-29

Speaker: Adélia Sequeira (Departamento de Matemática, IST)

As propriedades reológicas do sangue e dos seus elementos desempenham um papel fundamental na fisiologia da circulação sanguínea. ?? geralmente aceite, numa primeira aproximação, e em particular no que se refere à circulação vascular arterial, que o sangue se comporta como um meio contínuo,...

Paradoxos na epidemiologia das doenças infecciosas

2004-01-22

Speaker: Gabriela Gomes (Instituto Gulbenkian de Ciência)

As doenças infecciosas são cheias de surpresas. Porque é que a BCG protege certas populações da tuberculose pulmonar e não protege outras? Porque é que as intervenções contra a malária umas vezes funcionam e outras não? Porque é que em certos anos temos epidemias da gripe de dimensão e...

Métodos e ferramentas para programação semi-infinita não linear

2004-01-08

Speaker: Ismael Vaz (Departamento de Produção e Sistemas, Universidade do Minho)

Os problemas de programação semi-infinita (PSI) surgem nas mais diversas áreas da engenharia, como por exemplo, no controlo de poluição, no planeamento de trajectórias de robÎs, na determinação de conjuntos óptimos de sinais e na aproximação de Chebyshev. Os problemas de PSI são...

Métodos de análise de circuitos analógicos não-lineares

2003-11-27

Speaker: José Carlos Pedro (Universidade de Aveiro)

1 - Formulação do Problema da Simulação de Circuitos Analógicos Não-Lineares. 2 - O Método Natural: Integração da Equação Diferencial Ordinária no Domínio Temporal. Discretização da EDO e integração passo-a-passo. Problemas de Condições Iniciais e de Condições Fronteira. 3 - Método das...

SimEDO - Simulação de processos representados matematicamente por sistemas de Equações Diferenciais Ordinárias Não-lineares

2003-03-05

Speaker: Silvestre Dias Antunes (Dep. Eng. Mecânica, IST, Portugal)

O SimEDO é um programa inicialmente desenvolvido em 1982, para DOS, em Pascal (versão 1.0). Constituía um dos módulos de uma aplicação de ensino e controlo do ensino em PC. Em 1998, iniciou-se a sua revisão para o sistema operativo Windows, em Visual Basic. Pretende-se finalmente...

Ensino e Pesquisa em Modelagem de Sistemas Logísticos e de Transportes no Departamento de Engenharia e Transportes da Escola Politécnica da Universidade de São Paulo

2002-10-23

Speaker: Nicolau D.F. Gualda (Dep. Engenharia e Transportes, Escola Politénica, Universidade de São Paulo, Brasil)

Area(s): ...

Interpolation of Satellite Antenna Data

2002-10-04

Speaker: K. Salkauskas (University of Calgary, Canada)

In several papers originating within the Geophysics and Signal Processing community, the remote sensing of planet surface properties by antennae mounted on satellites is discussed. The mapping methods proposed there are based on a Backus-Gilbert theory. This is an interpolation theory based...

Robust portfolio selection

2002-06-24

Speaker: Reha TÌtÌncÌ (Carnegie Mellon University, USA)

We study the solution of mean-variance optimization problems for portfolio selection when the return and risk information is uncertain. We look for robust solutions, that is, solutions guaranteed to be good under all possible realizations of the uncertain parameters. We formulate these...

The primal-dual active set strategy as a semi-smooth Newton method

2002-04-18

Speaker: Michael Hintermuller (University of Graz, Áustria)

We focus on the primal-dual active set strategy, a versatile algorithmic tool in solving constrained optimal control problems, obstacle problems or, more generally, (linear) complementarity problems in function space settings. After reviewing its motivation by Moreau-Yosida type...

Convolution complementarity problems

2002-04-15

Speaker: David Stewart (University of Iowa, USA)

Convolution complementarity problems (CCP's) combine Linear Complementarity Problems with convolutions and differential equations. CCP's have the form $$ 0 \leq u(t) \perp (k*u)(t) + q(t) \geq 0 \qquad\mbox{for all } t$$ They are closely related to the Linear Complementarity Systems of...

Subspace optimization models and the graph partitioning problem

2002-04-15

Speaker: Suely Oliveira (University of Iowa, USA)

Parallel data distribution can be modeled as a Graph Partitioning Problem where we wish to divide a graph into subgraphs with roughly equal number of nodes with a mininum number of edges crossing between the subgraphs. This is a well-known NP-complete problem so heuristics need to be used....

Solitons, stability, instability and singularity formation

2002-03-21

Speaker: Jerry Bona (University of Illinois, Chicago, USA)

Area(s): ...

Non linear wave equations and the formation of sand bars

2002-03-21

Speaker: Jerry Bona (University of Illinois, Chicago, USA)

Area(s): ...

Level set methods for a 2D chemical problem

2001-12-20

Speaker: Stephane Clain (Universidade de Clairmont-Ferrant, França)

We present a numerical method to simulate the dissolution process of a solid plunged into a corrosive fluid. A level set formulation is presented to describe the free boundary evolution of the dissolution process. Our goal is to compute critical situations like the parting or the merge of...

Approximating the set of efficient points efficiently

2001-10-30

Speaker: Jörg Fliege (UniversitÀt Dortmund, Germany)

In multicriteria optimization, no point in the set of efficient points (the solution set) is able to represent the whole set: each efficient point is incomparable to each other one. Therefore, methods which can construct a representation of the whole set of efficient points are of particular...

On the convergence of solutions of discretized minimization problems

2001-09-12

Speaker: Rolf Dieter Grigorieff (Technical University Berlin, Germany)

In this talk elements of a discretization theory for minimization problems are presented. A characteristic feature of this theory is its relation to well-known theories tailored for applications to differential and integral equations, e.g. Ritz-Galerkin, colocation or finite difference...

Recovery of a density from the eigenvalues of a nonhomogeneous membrane

2001-06-01

Speaker: C. Maeve McCarthy (Murray State University, USA)

The vibrating elastic membrane is a classical problem in Mathematical Physics which arises in a wide variety of physical applications. Since the geometry of the membrane is usually well defined for a particular problem, determination of the nature of any nonhomogeneity is critical. The...

Finite difference and finite element methods for convection-dominated elliptic problems using layer adapted meshes

2001-05-25

Speaker: Hans-Goerg Roos (Institut fur Numeriche Mathematik, TU Dresden, Germany)

Area(s): ...

Superconvergence for triangular Raviart-Thomas elements

2001-05-04

Speaker: Jan Brandts (Universidade de Utrecht, Holand)

Area(s): ...

Superconvergence in mixed finite element methods

2001-05-04

Speaker: Jan Brandts (Universidade de Utrecht, Holand)

Area(s): ...

Problemas de contacto com atrito em grandes deformações

2001-04-04

Speaker: Luis Filipe Menezes (Univeridade de Coimbra, Portugal)

A modelação dos processos de enformação por deformação plástica conduz geralmente a problemas de fronteira bastante complicados, devido à forte não linearidade das leis de comportamento, à presença de grandes deformações e rotações e à evolução das condições de contacto com atrito. Esta...

Aplicações da optimização da topologia de estruturas ao projecto de materiais celulares e à remodelação óssea

2001-03-07

Speaker: Hélder Rodrigues (Instituto Superior Técnico, Lisboa, Portugal)

O modelo material para a optimização da topologia de estruturas aborda o seguinte problema de projecto: Para uma dada quantidade de material disponível qual é a sua distribuição, num domínio conhecido, que minimiza (maximiza) uma determinada função de custo e satisfaz um dado conjunto de...

Second order methods for solving the optimal output feedback design problem

2001-02-21

Speaker: El-Sayed Mostafa (University of Alexandria, Egypt and Univeridade de Coimbra, Portugal)

In this talk the problem of designing feedback control laws when a complete set of state variables is not available will be considered. For linear autonomous control systems with quadratic performance criterion, the design problem consists of choosing an approporiate static output feedback...

Utilizing the surrogate dual bound in capacity planning under economies of scale

2001-02-14

Speaker: Dennis Bricker (University of Iowa, USA)

Minimizing a nondecreasing separable concave cost function over a polyhedral set arises in capacity planning problems where economies of scale and fixed costs are significant, as well as production planning when a learning effect results in decreasing marginal costs. This is an NP-hard...

Nonlinear programming without second derivatives

2000-12-14

Speaker: Michael Wagner (Old Dominion University, Norfolk, USA)

We are interested in solving nonlinear programming problems by a Newton-like method without the need for second derivatives. The talk will start out by motivating the well-known SQP method for equality-constrained optimization and by discussing quasi-SQP variants that arise from...

An introduction to possibilistic optimization: theory, solution methods, comparisons and an application to radiation Therapy of Tumors

2000-10-04

Speaker: Weldon A. Lodwick (Fulbright Fellow, University of Coimbra and University of Colorado)

Optimization in the presence of various types of uncertainty in the values of parameters and ambiguity in the constraining relationships is introduced. Solution algorithms are discussed and one example is used to illustrate the similarities and differences among deterministic, stochastic and...

A globally convergent primal-dual interior-point filter method for nonconvex nonlinear programming

2000-09-20

Speaker: Michael Ulbrich (Technische UniversitÀt MÌnchen, Germany)

In this talk we show how the filter technique of Fletcher and Leyffer (1997) can be used to globalize a primal-dual interior-point Newton method for nonlinear programming. Filter methods apply the concept of dominance from bi-criteria optimization to handle the competing aims of minimizing...

A sensitivity and adjoint calculus for the optimal control of flows with shocks

2000-09-15

Speaker: Stefan Ulbrich (Technische UniversitÀt MÌnchen, Germany)

Optimal control or design problems for hyperbolic conservation laws arise for example in the design of ducts and airfoils or in the identification of friction parameters in shallow water flows after neglecting viscous effects. A key point for an efficient solution of the resulting...

Aproximação numérica de problemas de valores de fronteira singulares para equações de Emden-Fowler

2000-06-21

Speaker: Pedro Lima (Instituto Superior Técnico, Lisboa, Portugal)

No presente trabalho consideram-se problemas de valores de fronteira para um certo tipo de equações diferenciais ordinárias não-lineares de segunda ordem, conhecidas como equações generalizadas de Emden-Fowler. Estas equações têm numerosas aplicações, nomeadamente em problemas de mecânica de...

Emparelhamento em grafos e aplicações

2000-06-02

Speaker: Ilídia Coelho (Instituto Politécnico da Guarda, Portugal)

O primeiro estudo relacionado com emparelhamentos em grafos foi efectuado pelo matemático húngaro D. Konig que, em Abril de 1914, em Paris, no Congresso de Filosofia Matemática, apresentava uma comunicação onde referia que todo o grafo bipartido regular admitiria um emparelhamento perfeito....

Métodos baseados em subespaços de Krylov para grandes sistemas de equações lineares: caso não simétrico

2000-05-31

Speaker: Paulo Vasconcelos (Universidade do Porto, Portugal)

Area(s): ...

Uma pequena viagem aos mundos P e NP

2000-05-19

Speaker: Ana Maria de Almeida (Universidade de Coimbra, Portugal)

Existem problemas que não podem ser resolvidos por algoritmos e que se dizem, por isso mesmo, indecidíveis, mas muitos outros há para os quais é possível construir algoritmos para a sua resolução . No entanto, esses algoritmos possuem ``ordens de complexidade'' tão grandes que se dizem ser...

Métodos baseados em subespaços de Krylov para grandes sistemas de equações lineares: caso simétrico

2000-05-10

Speaker: Filomena d'Almeida (Universidade do Porto, Portugal)

Os métodos iterativos mais recomendados hoje em dia para a resolução de grandes sistemas, pela sua rapidez e convergência em grande número de casos, são os métodos baseados em subespaços de Krylov. A ideia base deste tipo de métodos é procurar uma solução aproximada para o sistema de...

Formulações para o problema da árvore de suporte de custo mínimo com restrição de capacidade

2000-04-07

Speaker: Pedro Coimbra Martins (ISCAC, Portugal)

Neste seminário serão analisadas algumas formulações conhecidas para o problema da determinação de uma árvore de suporte de custo minimo sobre um grafo, com uma restrição adicional que limita superiormente o número de nodos em cada subárvore incidente num determinado nodo desse grafo,...

Dois ou três minutos para descrever e resolver um problema linear

2000-03-31

Speaker: João Luís Soares (Universidade de Coimbra, Portugal)

Este seminário é particularmente dirigido aos alunos dos últimos anos da licenciatura ou bacharelato que possuem conhecimentos de Programação Linear. Recorrendo a exemplos, explicar-se-á como se pode resolver um programa linear usando o Microsoft Excel. Area(s): ...

A matrix-free method for the large-scale trust-region subproblem

2000-02-09

Speaker: Marielba Rojas (CERFACS, Toulouse, France)

We present a new method for the large-scale trust-region subproblem (TRS): minimize a quadratic function subject to a quadratic constraint. The method is matrix-free in the sense that only matrix-vector products are required. The new method is based on a reformulation of the TRS as a...

Interior-point methods for nonconvex problems

2000-01-26

Speaker: Francisco Javier Prieto (Dept. of Statistics and Econometrics, Univ. Carlos III, Madrid, Spain)

Interior-point methods are a very promising option for the solution of large-scale nonconvex optimization problems. The development of these methods is already well-advanced for the treatment of linear, quadratic and general convex problems. Recently, some algorithms have been proposed for...

Problema de Rayleigh-Bénard a duas componentes: estabilidade e modelação

2000-01-12

Speaker: Heitor Pina (Instituto Superior Técnico, Portugal)

Um lago solar é um dispositivo de armazenamento de energia solar que tira partido de um gradiente salino (estabilizador) que contraria um gradiente térmico (desestabilizador). Assim, é importante determinar as condições de estabilidade do lago bem como proceder à sua modelação com vista a...

Uma instabilidade de Godunov-Ryabenkii

2000-01-05

Speaker: Ercília Sousa (Universidade de Coimbra, Portugal and Oxford University, UK)

Consideramos um método de diferenças finitas para a equação de convecção difusão. Este método será sujeito a determinadas condições de fronteira, que darão origem a fenómenos de instabilidade, que serão explicados utilizando a teoria de Godunov-Ryabenkii. Area(s): ...

Qualocation with pseudodifferential operators using multiple knot periodic splines

Speaker: R.D. Grigorieff (TU Berlin)

Global properties of epidemiological models and virus dynamics models with nonlinear incidence rates by Lyapunov direct method

Speaker: Andrei Korobeinikov (University of Limerick)

Seminars - Historic

Structure-preserving integrators in Poisson geometry

A brief introduction to Machine Learning: from the perceptron to large language models

Dynamics and stability of a network human-landscape model

Advances in finite volume methods for the simulation of flows in porous media

A low-cost algorithm to determine spacecraft trajectories in CR3BP

Scientific machine learning: some methods and applications

Scalable methods for high-dimensional inverse problems using neural networks and implicit method of moments

High order methods for PDE: panorama and perspective

A low-cost alternating projection approach for a continuous formulation of convex and cardinality constrained optimization

Asymptotic behavior and stability of solutions in differential equations of mixed type

K dissimilar paths

Recent results on planar predator-prey and competitive models with seasonality

How can the Cerebral Aneurysms near-wall region be investigated?

A multi-scale biological description with application to autoimmune diseases

Feedback control of falling liquid films using a hierarchical model approach

Stochastic optimization of multiple objectives and fairness in machine learning

Symbolic data and optimization

Model-based evaluation of school- and non-school based public health measures on controlling the COVID-19 pandemic in the Netherlands

Complex network of epidemic models

Mathematical modelling in solid mechanics: an example with fracking

Mathematical models and methods for Breach Formation in Earth Embankment Dams

Is fractional calculus the ultimate solution to all anomalous-diffusion problems?

Optimization meets Medical Physics: tailored algorithms

The Method of Fundamental Solutions and its application for solving shape optimization problems

Matrix functions: applications, computation and topics of research

Multiobjective optimization: fundamentals and an application in demand response

Peregrine's system revisited

The finite element method in sheet metal forming simulation

Stochastic solutions for nonlinear partial differential equations

Portfolio selection in evolutionary algorithms

Performance estimation of first-order methods for composite convex optimization

Efficient and accurate Lagrangian-Eulerian numerical schemes for solving hyperbolic balance laws

Numerical modelling of cell-renewal, pit patterns and crypt fission in colonic crypts

A problem-dependent inner approximation of the completely positive cone

Mining chemical space for pharmacological rules: corneal permeation as an example

Multiscale non-helical dynamos

Numerical simulation of wave propagation from deep waters to very shallow waters, including changes over real bottoms

Application of data mining to structural biology

Time-analyticity of fluid particle trajectories in ideal fluid flow

Oscillatory and nonoscillatory behavior of a differential delay system of order n

Early exercise boundaries for American-style knock-out options

The \(\theta\)-parareal schemes

Fast algorithms for high frequency wave propagation

Volterra integral equations for non linear partial differential equations of integrable type

Renormalized transport of inertial particles

Constrained partitions in graphs: bio and financial applications

Optimal simplex finite-element approximations of arbitrary order in curved domains circumventing the isoparametric technique

Systems of partial differential equations arising from population dynamics and neuroscience: Free boundary problems as a result of segregation

A short survey on Copositive and Completely Positive optimization

The p-median on disconnected graphs

Implementing a stable version of the tau method in a toolbox

Finite difference methods for the reaction-wave-diffusion equation with distributed order in time

Biology and Mathematics: a strategic alliance against cancer through new anti-tumoral therapies

Numerical investigations of spatially segregation models

On mixed and stabilized finite element methods for the obstacle problem

Computational modeling of hematopoietic stem/progenitor cells expansion and differentiation

Exponential splitting methods for the time integration of the Klein-Gordon equation with Hagstrom-Warburton high-order absorbing boundary conditions

From medical images to computational hemodynamics: a robust pipeline

A numerical solution for a governing equation of Lévy motion

A coupled release-absorption model for drug delivery systems

Object detection, multispectral fusion, motion analysis and tracking in aerial imagery and video

Filtering, fusion, detection and segmentation of microvasculature vessel fluorescence imagery

On computing efficient pairs of disjoint paths

Modeling Dengue disease: two real outbreaks - theoretical and practical issues

Quaternion Newton-like methods

Wavelets in Economics and Political Science

Harmonic Analysis for the Natural Sciences

Computational hydrodynamics, from theory to practice

Assessment of image derived PET quantification techniques

Modeling blood flow and mass transport by a drug eluting stent

Some recent mathematical ideas for applications in biology

Numerical modeling of complex fluid flows using the Finite Volume Method

Constrained optimization techniques for quadratic matrix model updating

The MOOD method, principle and (some) examples

Computational methods in the fractional calculus of variations

On approximation by periodic splines: theory and application

Optimal basis algorithm and its application to matrix scaling

Non-Fickian models for biodegradable drug eluting stents

Explicit Leap-frog DG method for time domain electromagnetic wave propagation