Hi David, thanks for the fast answer.

Am 16.06.2010 um 09:34 schrieb David Bellot:

better to give the same size to x and y, filling x with extra zeros.

I can't do this, because I need a "grow up" for my matrix. I have a symmetric matrix with NxN

elements and in a next step the matrix must grow up to (N+1)x(N+1)

here z takes the size of y but is filled with wrong indices due to x having a smaller size.

By the way, I have never been so confortable with the idea of assuming zeros when adding 2 matrices of different sizes :-)

That's only a test and my elements of x and y aren't be zero in reality