Orthogonal symmetric matrices and joins of graphs
 
 
Description:  We ask when is the join of two (possibly disconnected) graphs G and H the pattern of an orthogonal symmetric matrix. A notion of compatibility for multiplicity matrices gives rise to a necessary condition. To address sufficiency, we introduce generic realisability that generalises the concept of nowhere-zero eigenbasis. As an application, we resolve the question in the case when G and H are both unions of complete graphs.
Date:  2021-09-22
Start Time:   14:30
Speaker:  Helena Smigoc (Univ. College Dublin, Ireland)
Institution:  University College Dublin
Place:  Zoom: https://videoconf-colibri.zoom.us/j/81787306524
Research Groups: -Algebra and Combinatorics
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