set some diagonal elements of a matrix in Matlab

Question

A quick question, I have a sparse matrix A and a index list b = [2, 3, 4 ...] , I want to set A(2, 2), A(3, 3), A(4, 4)... = 0 . I tried A(b, b) = 0, the result is that A(2, 3), A(2, 4), A(3, 2), A(3, 4), A(4, 2), A(4, 3) and some non-diagonal elements of this matrix are also set zero, how to deal with that?

Answer 1

Use linear indexing :

A(sub2ind(size(A),b,b)) = 0;

This works for full or sparse matrices.