Matrix condition number question

[tim51]

Hey,

I've been studying condition numbers for matrices. I found a past exam question that asks if the notion of condition numbers can be used for non-square matrices.

Intuitively I thought it couldn't because cond(A) = ||A||.||A^-1|| and non-square matrices have no inverse. But matlab will calculate it?

Why do condition numbers exist for non-square matricies and do they have any meaning at all?

Thanks.

[hotvette]

Least squares analysis involves non-square matrices and condition number is a meaure of rank deficiency.