int ranbinom(int n, double p)
{
/**
Knuth Vol 2, p 131
*/
#define BTHRESH 50
int a, b ;
double x ;
if (p>=1) return n ;
if (p<=0) return 0 ;
if (n<=0) return 0 ;
if (n<=BTHRESH) {
return ranb1(n,p) ; /** small case */
}
a = 1 + n/2 ;
b = n + 1 - a ;
x = ranbeta((double) a, (double) b) ;
if (x>=p) return ranbinom(a-1, p/x) ;
return (a + ranbinom(b-1, (p-x)/(1.0-x)) ) ;
}
static void vbinom(long count, double n[], long lengthN,
double p[], long lengthP, double * rvec)
{
long i, iN, iP;
long incN = (lengthN == 1) ? 0 : 1;
long incP = (lengthP == 1) ? 0 : 1;
WHERE("vbinom");
for (i = iN = iP = 0; i < count; i++, iN += incN, iP += incP)
{
rvec[i] = ranbinom((long) n[iN], p[iP]);
} /*for (i = 0; i < count; i++)*/
} /*vbinom()*/
void ranmultinom(int *samp, int n, double *p, int len)
// multinomial sample p is prob dist n samples returned
// work is O(len^2) which is silly
{
int x ;
double *pp ;
if (len==0) return ;
ivzero(samp, len) ;
if (n<=0) return ;
if (len==1) {
samp[0] = n ;
return ;
}
ZALLOC(pp, len, double) ;
copyarr(p, pp, len) ;
bal1(pp, len) ;
samp[0] = x = ranbinom(n, pp[0]) ;
ranmultinom(samp+1, n-x, p+1, len-1) ;
free(pp) ;
}
