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## Summary:

- how do be sure a matrix is invertible

## Main Question or Discussion Point

Hello

Suppose if have a matrix that is purely diagonal with NO zeros: M (which is n by n -square)

Suppose I have another matrix the contains coordinate information, call it A.

This one is NOT a square matrix, but, (n by m) (where, in general m < n)

I form this: Q = A-transpose * M * A

(where Q is, of course, m by m)

How can I be sure Q is invertible?

Suppose if have a matrix that is purely diagonal with NO zeros: M (which is n by n -square)

Suppose I have another matrix the contains coordinate information, call it A.

This one is NOT a square matrix, but, (n by m) (where, in general m < n)

I form this: Q = A-transpose * M * A

(where Q is, of course, m by m)

How can I be sure Q is invertible?