3 * Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 James Theiler, Brian Gough
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13 * General Public License for more details.
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17 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
22 #include <gsl/gsl_rng.h>
23 #include <gsl/gsl_randist.h>
24 #include <gsl/gsl_sf_gamma.h>
26 /* The hypergeometric distribution has the form,
28 prob(k) = choose(n1,t) choose(n2, t-k) / choose(n1+n2,t)
30 where choose(a,b) = a!/(b!(a-b)!)
32 n1 + n2 is the total population (tagged plus untagged)
33 n1 is the tagged population
34 t is the number of samples taken (without replacement)
35 k is the number of tagged samples found
40 gsl_ran_hypergeometric (const gsl_rng * r, unsigned int n1, unsigned int n2,
43 const unsigned int n = n1 + n2;
47 unsigned int b = n1 + n2;
57 for (i = 0 ; i < t ; i++)
59 double u = gsl_rng_uniform(r) ;
74 for (i = 0 ; i < n - t ; i++)
76 double u = gsl_rng_uniform(r) ;
94 gsl_ran_hypergeometric_pdf (const unsigned int k,
95 const unsigned int n1,
96 const unsigned int n2,
108 else if (t > n2 && k + n2 < t )
116 double c1 = gsl_sf_lnchoose(n1,k);
117 double c2 = gsl_sf_lnchoose(n2,t-k);
118 double c3 = gsl_sf_lnchoose(n1+n2,t);
120 p = exp(c1 + c2 - c3) ;