how to prove it?
I am talking about matrixes which:
( Ax , x ) > 0 for any x not equals 0.
How to prove, that AT is also positive?
xT * A * x = ( xT * A * x )T
Hint: Write the inner product as $x^T A x$ and use the fact that that expression is its own transpose (since it's a 1-by-1 matrix).