41 lines
889 B
C++
41 lines
889 B
C++
#include "nr.h"
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void NR::simpr(Vec_I_DP &y, Vec_I_DP &dydx, Vec_I_DP &dfdx, Mat_I_DP &dfdy,
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const DP xs, const DP htot, const int nstep, Vec_O_DP &yout,
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void derivs(const DP, Vec_I_DP &, Vec_O_DP &))
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{
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int i,j,nn;
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DP d,h,x;
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int n=y.size();
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Mat_DP a(n,n);
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Vec_INT indx(n);
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Vec_DP del(n),ytemp(n);
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h=htot/nstep;
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for (i=0;i<n;i++) {
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for (j=0;j<n;j++) a[i][j] = -h*dfdy[i][j];
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++a[i][i];
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}
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ludcmp(a,indx,d);
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for (i=0;i<n;i++)
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yout[i]=h*(dydx[i]+h*dfdx[i]);
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lubksb(a,indx,yout);
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for (i=0;i<n;i++)
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ytemp[i]=y[i]+(del[i]=yout[i]);
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x=xs+h;
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derivs(x,ytemp,yout);
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for (nn=2;nn<=nstep;nn++) {
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for (i=0;i<n;i++)
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yout[i]=h*yout[i]-del[i];
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lubksb(a,indx,yout);
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for (i=0;i<n;i++) ytemp[i] += (del[i] += 2.0*yout[i]);
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x += h;
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derivs(x,ytemp,yout);
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}
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for (i=0;i<n;i++)
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yout[i]=h*yout[i]-del[i];
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lubksb(a,indx,yout);
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for (i=0;i<n;i++)
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yout[i] += ytemp[i];
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}
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