Calculate hessian matrix of sh expansion #356

Hi,

I'm wondering if (or how) it were possible to retrieve the hessian matrix from an existing set of spherical harmonics coefficients. In more detail, I am looking for a way to calculate mean and gaussian curvatures, which, in turn I can calculate from the main first and second order derivates. I saw that DHGradient() already calculates the first order derivatives - what would be the best way to get the hessian matrix from this?

Thanks in advance!