This is a recursive function to compute the multinomial coefficient of
(x0+x1+...+xm-1)^N The goal of this function is to find every
{k0,...,km-1} as k0+...+km-1=N (cf multinomial theorem on Wikipedia for
more understanding the formula) parameters : index= array of the ki,
size= number f coefficient ki, coefMax= the maximum value that a ki can
take, it= the iteration of the recursive function, m= dilation factor,
N=order of the spline, h=mask