40 lines
627 B
C++
40 lines
627 B
C++
#include <cmath>
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#include "nr.h"
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using namespace std;
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DP NR::poidev(const DP xm, int &idum)
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{
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const DP PI=3.141592653589793238;
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static DP sq,alxm,g,oldm=(-1.0);
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DP 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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