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This commit is contained in:
Gabriele Cosmo
2020-06-26 10:23:25 +02:00
parent c02c370437
commit 67ba86d073
1871 changed files with 174422 additions and 131884 deletions
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source/parameterisations/gflash/src/Gamma.cc
+8 -42
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@@ -40,19 +40,10 @@ MyGamma::~MyGamma(){}
//____________________________________________________________________________
double MyGamma::Gamma(double z)
{
// Computation of gamma(z) for all z>0.
//
// The algorithm is based on the article by C.Lanczos [1] as denoted in
// Numerical Recipes 2nd ed. on p. 207 (W.H.Press et al.).
//
// [1] C.Lanczos, SIAM Journal of Numerical Analysis B1 (1964), 86.
//
//--- Nve 14-nov-1998 UU-SAP Utrecht
if (z<=0) return 0;
double v = LnGamma(z);
return std::exp(v);
if (z <= 0)
return 0;
return std::tgamma(z);
}
//____________________________________________________________________________
@@ -145,33 +136,8 @@ double MyGamma::GamSer(double a,double x)
double MyGamma::LnGamma(double z)
{
// Computation of ln[gamma(z)] for all z>0.
//
// The algorithm is based on the article by C.Lanczos [1] as denoted in
// Numerical Recipes 2nd ed. on p. 207 (W.H.Press et al.).
//
// [1] C.Lanczos, SIAM Journal of Numerical Analysis B1 (1964), 86.
//
// The accuracy of the result is better than 2e-10.
//
//--- Nve 14-nov-1998 UU-SAP Utrecht
if (z<=0) return 0;
// Coefficients for the series expansion
double c[7] = { 2.5066282746310005, 76.18009172947146, -86.50532032941677
,24.01409824083091, -1.231739572450155, 0.1208650973866179e-2
,-0.5395239384953e-5};
double x = z;
double y = x;
double tmp = x+5.5;
tmp = (x+0.5)*Log(tmp)-tmp;
double ser = 1.000000000190015;
for (int i=1; i<7; i++) {
y += 1;
ser += c[i]/y;
}
double v = tmp+Log(c[0]*ser/x);
return v;
if (z <= 0)
return 0;
return std::lgamma(z);
}