Congruence of matrix spaces, matrix tuples, and multilinear maps

Abstract

Two matrix vector spaces V,W⊂Cn×n are said to be equivalent if SVR=W for some nonsingular S and R. These spaces are congruent if R=ST. We prove that if all matrices in V and W are symmetric, or all matrices in V and W are skew-symmetric, then V and W are congruent if and only if they are equivalent.Let F:U×…×U→V and G:U′×…×U′→V′ be symmetric or skew-symmetric k-linear maps over C. If there exists a set of linear bijections φ1,…,φk:U→U′ and ψ:V→V′ that transforms F to G, then there exists such a set with φ1=…=φk.