$x_1, x_2 > 0$
$f(x_1,x_2) = \frac{1}{x_1^3x_2}$
Is this function convex?
I think it is because Hessian matrix is $$\begin{pmatrix} \frac{12}{x_1^5x_2} & \frac{3}{x_1^4x_2^2} \\ \frac{3}{x_1^4x_2^2} & \frac{2}{x_1^3x_2^3}\end{pmatrix}$$
How do i show that the matrix is positive? multiply it by vector a^T and a isn't working..
Thanks!
can i just say its positive cause every element is positive?
