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