50 lines
1000 B
C
50 lines
1000 B
C
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#include <math.h>
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#define NRANSI
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#include "nrutil.h"
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#define ERRTOL 0.08
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#define TINY 1.5e-38
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#define BIG 3.0e37
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#define THIRD (1.0/3.0)
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#define C1 (1.0/24.0)
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#define C2 0.1
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#define C3 (3.0/44.0)
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#define C4 (1.0/14.0)
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float rf(float x, float y, float z)
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{
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float alamb,ave,delx,dely,delz,e2,e3,sqrtx,sqrty,sqrtz,xt,yt,zt;
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if (FMIN(FMIN(x,y),z) < 0.0 || FMIN(FMIN(x+y,x+z),y+z) < TINY ||
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FMAX(FMAX(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 (FMAX(FMAX(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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#undef ERRTOL
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#undef TINY
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#undef BIG
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#undef THIRD
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#undef C1
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#undef C2
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#undef C3
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#undef C4
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#undef NRANSI
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