42 lines
705 B
C++
42 lines
705 B
C++
#include <cmath>
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#include "nr.h"
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using namespace std;
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void NR::ratint(Vec_I_DP &xa, Vec_I_DP &ya, const DP x, DP &y, DP &dy)
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{
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const DP TINY=1.0e-25;
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int m,i,ns=0;
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DP w,t,hh,h,dd;
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int n=xa.size();
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Vec_DP c(n),d(n);
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hh=fabs(x-xa[0]);
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for (i=0;i<n;i++) {
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h=fabs(x-xa[i]);
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if (h == 0.0) {
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y=ya[i];
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dy=0.0;
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return;
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} else if (h < hh) {
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ns=i;
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hh=h;
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}
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c[i]=ya[i];
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d[i]=ya[i]+TINY;
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}
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y=ya[ns--];
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for (m=1;m<n;m++) {
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for (i=0;i<n-m;i++) {
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w=c[i+1]-d[i];
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h=xa[i+m]-x;
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t=(xa[i]-x)*d[i]/h;
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dd=t-c[i+1];
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if (dd == 0.0) nrerror("Error in routine ratint");
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dd=w/dd;
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d[i]=c[i+1]*dd;
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c[i]=t*dd;
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}
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y += (dy=(2*(ns+1) < (n-m) ? c[ns+1] : d[ns--]));
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}
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}
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