34 lines
853 B
C++
34 lines
853 B
C++
#include <cmath>
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#include "nr.h"
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using namespace std;
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DP NR::rf(const DP x, const DP y, const DP z)
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{
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const DP ERRTOL=0.0025, TINY=1.5e-38, BIG=3.0e37, THIRD=1.0/3.0;
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const DP C1=1.0/24.0, C2=0.1, C3=3.0/44.0, C4=1.0/14.0;
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DP alamb,ave,delx,dely,delz,e2,e3,sqrtx,sqrty,sqrtz,xt,yt,zt;
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if (MIN(MIN(x,y),z) < 0.0 || MIN(MIN(x+y,x+z),y+z) < TINY ||
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MAX(MAX(x,y),z) > BIG)
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nrerror("invalid arguments in rf");
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xt=x;
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yt=y;
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zt=z;
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do {
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sqrtx=sqrt(xt);
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sqrty=sqrt(yt);
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sqrtz=sqrt(zt);
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alamb=sqrtx*(sqrty+sqrtz)+sqrty*sqrtz;
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xt=0.25*(xt+alamb);
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yt=0.25*(yt+alamb);
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zt=0.25*(zt+alamb);
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ave=THIRD*(xt+yt+zt);
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delx=(ave-xt)/ave;
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dely=(ave-yt)/ave;
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delz=(ave-zt)/ave;
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} while (MAX(MAX(fabs(delx),fabs(dely)),fabs(delz)) > ERRTOL);
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e2=delx*dely-delz*delz;
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e3=delx*dely*delz;
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return (1.0+(C1*e2-C2-C3*e3)*e2+C4*e3)/sqrt(ave);
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}
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