double loghprob(int n, int a, int m, int k)
// http://www.math.uah.edu/stat/urn/Hypergeometric.xhtml
{
/**
n balls a black. Pick m without replacement
return log prob (k black)
*/
double ytop, ybot ;
if (k<0) return -1.0e30 ;
if (k>a) return -1.0e30 ;
if (k>m) return -1.0e30 ;
if ((m-k)>(n-a)) return -1.0e30 ;
ytop = logbino(a, k) + logbino(n-a, m-k) ;
ybot = logbino(n, m) ;
return ytop - ybot ;
}
double logmultinom(int *cc, int n)
/* log multinomial */
{
int t, k, i ;
double y, ytot ;
if (n<=1) return 0.0 ;
t = intsum(cc, n) ;
if (t==0) return 0.0 ;
ytot = 0 ;
for (i=0; i<n-1; i++) {
k = cc[i] ;
y = logbino(t,k) ;
ytot += y ;
t -= k ;
}
return ytot ;
}
