Variance benchmark

[Nelson-numerical-software]

A small benchmark about variance function:

B = []; N = 6000; A=1:N*N; A = reshape(A,N,N);
tic(); B = var(A); toc()

B = []; N = 6000; A = 1:N*N; A = matrix(A,N,N);
tic(); B = mtlb_var(A);toc