18 lines
383 B
C++
18 lines
383 B
C++
#include <cmath>
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#include "nr.h"
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using namespace std;
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DP NR::betai(const DP a, const DP b, const DP x)
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{
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DP bt;
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if (x < 0.0 || x > 1.0) nrerror("Bad x in routine betai");
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if (x == 0.0 || x == 1.0) bt=0.0;
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else
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bt=exp(gammln(a+b)-gammln(a)-gammln(b)+a*log(x)+b*log(1.0-x));
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if (x < (a+1.0)/(a+b+2.0))
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return bt*betacf(a,b,x)/a;
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else
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return 1.0-bt*betacf(b,a,1.0-x)/b;
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}
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