For a positive semi-definite matrix $C$, I want to find the solution to the following problem:
$\arg\max_{h\geq 0} h^T C h\quad$ s.t. $\quad h^T h\leq 1$
Any pointers are welcome.
The magic words are quadratically constrained quadratic programming. And semidefinite programming.
EDIT I misread the question (it is a convex maximization problem). This is still somewhat tractable in practice (since the objective still has convex epigraphs), but see the excellent answer by @NoahStein to this question.