/**
* Description not yet available.
* \param
*/
double randnegbinomial(double mu,double tau,
const random_number_generator& rng)
{
if (tau<=1.0)
{
cerr << "Error in randnegbinomial overdispersion must be >=1" << endl;
ad_exit(1);
}
double r=mu/(tau-1);
double c=r/mu;
double z=sgamma(r,rng);
double lambda=z/c;
return randpoisson(lambda,rng);
}
double gengam(lua_RNG *o,double a,double r)
/*
**********************************************************************
GENerates random deviates from GAMma distribution
Function
Generates random deviates from the gamma distribution whose
density is
(A**R)/Gamma(R) * X**(R-1) * Exp(-A*X)
Arguments
a --> Location parameter of Gamma distribution
r --> Shape parameter of Gamma distribution
Method
Renames SGAMMA from TOMS as slightly modified by BWB to use RANF
instead of SUNIF.
For details see:
(Case R >= 1.0)
Ahrens, J.H. and Dieter, U.
Generating Gamma Variates by a
Modified Rejection Technique.
Comm. ACM, 25,1 (Jan. 1982), 47 - 54.
Algorithm GD
(Case 0.0 <= R <= 1.0)
Ahrens, J.H. and Dieter, U.
Computer Methods for Sampling from Gamma,
Beta, Poisson and Binomial Distributions.
Computing, 12 (1974), 223-246/
Adapted algorithm GS.
**********************************************************************
*/
{
static double gengam;
gengam = sgamma(o,r);
gengam /= a;
return gengam;
}
