35 lines
619 B
C++
35 lines
619 B
C++
#include <cmath>
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#include "nr.h"
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using namespace std;
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void NR::polint(Vec_I_DP &xa, Vec_I_DP &ya, const DP x, DP &y, DP &dy)
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{
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int i,m,ns=0;
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DP den,dif,dift,ho,hp,w;
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int n=xa.size();
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Vec_DP c(n),d(n);
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dif=fabs(x-xa[0]);
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for (i=0;i<n;i++) {
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if ((dift=fabs(x-xa[i])) < dif) {
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ns=i;
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dif=dift;
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}
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c[i]=ya[i];
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d[i]=ya[i];
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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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ho=xa[i]-x;
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hp=xa[i+m]-x;
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w=c[i+1]-d[i];
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if ((den=ho-hp) == 0.0) nrerror("Error in routine polint");
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den=w/den;
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d[i]=hp*den;
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c[i]=ho*den;
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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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