  We prove a condition on f \in C^2(\R+,\R) for the convexity of (f o det) on
PSym(n), namely that f o det is convex on PSym(n) if and only if
f"(s)+(n-1)/(ns) f'(s) >= 0 and f'(s)<= 0 \forall s \in \R+. This generalizes
the observation that C --> -ln det C is convex as a function of C.
