finite symmetric difference Hessiann
H=hessian(func,pin[,arg1, argn])
* func= (minus likelihood) function to minimize
* pin= parameter vector fed to func
* argi=
- 'maxit=x' to set the maximum # of iterations (default = 500)
- arguments of function func others that the parameters
* H= value of the hessian of namefunc at point grocer_p
b = parameter vector (k x 1)
varargin = arguments passed to the function