MATLAB: Standar deviation of a matrix (specific elements)

Question

Dear friends

I want to obtain the standar deviation of a square matrix but only off-diagonal elements. anyone could help me?

Thanks!

Answer 1

Two ways, both producing the same value:

M = rand(7);                        % Create Data
diagM = nan(1,size(M,1));
M = M + diag(diagM);
Mmean1 = mean(M(:),'omitnan');
Mmean2 = mean(M(~isnan(M(:))));