[FIXED] Check if a large matrix is diagonal matrix in python

Issue

I have compute a very large matrix M with lots of degenerate eigenvectors(different eigenvectors with same eigenvalues). I use QR decomposition to make sure these eigenvectors are orthonormal, so the Q is the orthonormal eigenvectors of M, and Q^{-1}MQ = D, where D is diagonal matrix. Now I want to check if D is truly diagonal matrix, but when I print D, the matrix is too large to show all of them, so how can I know if it is truly diagonal matrix?

Solution

Remove the diagonal and count the non zero elements:

np.count_nonzero(x - np.diag(np.diagonal(x)))

Answered By - donkopotamus