Check if a matrix is an identity matrix in Matlab

Question

I need to check if a matrix is an identity matrix. I know there's a function which check if a matrix is a diagonal matrix, that is, isdiag. I know I can do the following to check if a matrix a is an identity matrix:

isequal(a, eye(size(a, 1)))

Is there a function like isdiag tha does it directly for me?

Answer 1

As others have said, you don't necessarily want to check for exact equality to the identity matrix. Also using eye can potentially take up an unnecessary amount of memory for sufficiently large matrices. I would recommend using diag to get around that.

isdiag(a) && all(abs(diag(a) - 1) < tolerance)

Answer 2

sum(sum(A - eye(size(A,1)) < epsilon)) == 0

Subtract by identity and check if any elements are greater than epsilon.