38 lines
608 B
C
38 lines
608 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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#define FPMIN 1.0e-30
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void gcf(gammcf,a,x,gln)
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float *gammcf,*gln,a,x;
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{
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float gammln();
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void nrerror();
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int i;
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float an,b,c,d,del,h;
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*gln=gammln(a);
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b=x+1.0-a;
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c=1.0/FPMIN;
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d=1.0/b;
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h=d;
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for (i=1;i<=ITMAX;i++) {
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an = -i*(i-a);
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b += 2.0;
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d=an*d+b;
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if (fabs(d) < FPMIN) d=FPMIN;
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c=b+an/c;
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if (fabs(c) < FPMIN) c=FPMIN;
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d=1.0/d;
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del=d*c;
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h *= del;
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if (fabs(del-1.0) < EPS) break;
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}
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if (i > ITMAX) nrerror("a too large, ITMAX too small in gcf");
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*gammcf=exp(-x+a*log(x)-(*gln))*h;
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}
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#undef ITMAX
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#undef EPS
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#undef FPMIN
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