35 lines
603 B
C++
35 lines
603 B
C++
#include <cmath>
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#include "nr.h"
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using namespace std;
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void NR::gauleg(const DP x1, const DP x2, Vec_O_DP &x, Vec_O_DP &w)
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{
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const DP EPS=1.0e-14;
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int m,j,i;
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DP z1,z,xm,xl,pp,p3,p2,p1;
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int n=x.size();
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m=(n+1)/2;
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xm=0.5*(x2+x1);
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xl=0.5*(x2-x1);
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for (i=0;i<m;i++) {
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z=cos(3.141592654*(i+0.75)/(n+0.5));
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do {
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p1=1.0;
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p2=0.0;
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for (j=0;j<n;j++) {
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p3=p2;
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p2=p1;
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p1=((2.0*j+1.0)*z*p2-j*p3)/(j+1);
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}
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pp=n*(z*p1-p2)/(z*z-1.0);
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z1=z;
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z=z1-p1/pp;
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} while (fabs(z-z1) > EPS);
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x[i]=xm-xl*z;
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x[n-1-i]=xm+xl*z;
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w[i]=2.0*xl/((1.0-z*z)*pp*pp);
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w[n-1-i]=w[i];
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}
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}
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