37 lines
585 B
C
37 lines
585 B
C
|
|
#include <math.h>
|
|
#define ITMAX 100
|
|
#define EPS 3.0e-7
|
|
|
|
void gser(gamser,a,x,gln)
|
|
float *gamser,*gln,a,x;
|
|
{
|
|
float gammln();
|
|
void nrerror();
|
|
int n;
|
|
float sum,del,ap;
|
|
|
|
*gln=gammln(a);
|
|
if (x <= 0.0) {
|
|
if (x < 0.0) nrerror("x less than 0 in routine gser");
|
|
*gamser=0.0;
|
|
return;
|
|
} else {
|
|
ap=a;
|
|
del=sum=1.0/a;
|
|
for (n=1;n<=ITMAX;n++) {
|
|
++ap;
|
|
del *= x/ap;
|
|
sum += del;
|
|
if (fabs(del) < fabs(sum)*EPS) {
|
|
*gamser=sum*exp(-x+a*log(x)-(*gln));
|
|
return;
|
|
}
|
|
}
|
|
nrerror("a too large, ITMAX too small in routine gser");
|
|
return;
|
|
}
|
|
}
|
|
#undef ITMAX
|
|
#undef EPS
|