43 lines
624 B
C
43 lines
624 B
C
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#include <math.h>
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#define PI 3.141592654
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float poidev(xm,idum)
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float xm;
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long *idum;
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{
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float gammln(),ran1();
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static float sq,alxm,g,oldm=(-1.0);
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float em,t,y;
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if (xm < 12.0) {
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if (xm != oldm) {
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oldm=xm;
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g=exp(-xm);
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}
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em = -1;
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t=1.0;
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do {
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++em;
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t *= ran1(idum);
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} while (t > g);
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} else {
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if (xm != oldm) {
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oldm=xm;
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sq=sqrt(2.0*xm);
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alxm=log(xm);
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g=xm*alxm-gammln(xm+1.0);
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}
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do {
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do {
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y=tan(PI*ran1(idum));
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em=sq*y+xm;
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} while (em < 0.0);
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em=floor(em);
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t=0.9*(1.0+y*y)*exp(em*alxm-gammln(em+1.0)-g);
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} while (ran1(idum) > t);
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}
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return em;
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}
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#undef PI
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