How to generalize the size of identity matrix as that of any size of input matrix

My input matrix M of size 5X5, I want an identity matrix of its size so I gave I=ones(5).I have to change every time the size of identity matrix to that of the size of input matrix.

I want generalized way of identity matrix any help regarding this query please.

Answer 1

[Walter Roberson]

eye(length(M))