positive definite matrix predicate

Hello ! I have a lot of questions :-)

Trying to implement a certain special function in Axiom (Epstein zeta, to be 
precise), which depends on a positive definite matrix argument. How do I 
properly implement the test that the matrix is positive definite ?

Did I overlook a standard predicate, which tests for this ? Should I perform 
the test in my function (which, since such a test seems to be quite basis, 
may potentially lead to duplication of code in future) and potentially fail ? 
If I add such predicate to MatrixCategory (which looks like a proper place 
for such a basic thing), what are the conditions for the patch to be 
accepted ?

With the best regards,
                          Konstantin.