Say, this seems trivial, but my small brain can't find anything simple, and what I thought would work definitely does not. I can't find any solutions that are well applicable to this problem either...basically I want to take a desired matrix, say `{{1, 0},{0,1}}` and compare it to a list of matrices to find some form of an error rate/measure of difference between them.
Subtract[Abs[{{w, x}, {y, z}}]^2, Abs[{{a, b}, {c, d}}]^2]
works but neither
Subtract[Abs[{{w, x}, {y, z}}]^2, #] & /@ Abs[{{{a, b}, {c, d}}, {{e, f}, {g, h}}}]^2