/* From Press, et al., Numerical Recipes */
static void
poisson_rejection (double lambda, double *p, size_t n)
{
double sq = sqrt(2.0*lambda);
double alxm = log(lambda);
double g = lambda*alxm - LGAMMA(lambda+1.0);
size_t i;
for (i = 0; i < n; i++)
{
double y, em, t;
do {
do {
y = tan(M_PI*RUNI);
em = sq * y + lambda;
} while (em < 0.0);
em = floor(em);
t = 0.9*(1.0+y*y)*exp(em*alxm-flogfak(em)-g);
} while (RUNI > t);
p[i] = em;
}
}
/* for migrate this is defined in tools.h */
MYREAL
logfac (long n)
{
/* log(n!) values were calculated with Mathematica
with a precision of 30 digits */
switch (n)
{
case 0:
return 0.;
case 1:
return 0.;
case 2:
return 0.693147180559945309417232121458;
case 3:
return 1.791759469228055000812477358381;
case 4:
return 3.1780538303479456196469416013;
case 5:
return 4.78749174278204599424770093452;
case 6:
return 6.5792512120101009950601782929;
case 7:
return 8.52516136106541430016553103635;
case 8:
return 10.60460290274525022841722740072;
case 9:
return 12.80182748008146961120771787457;
case 10:
return 15.10441257307551529522570932925;
case 11:
return 17.50230784587388583928765290722;
case 12:
return 19.98721449566188614951736238706;
default:
return LGAMMA (n + 1.);
}
}
