34 lines
657 B
C++
34 lines
657 B
C++
#include "nr.h"
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void NR::stoerm(Vec_I_DP &y, Vec_I_DP &d2y, const DP xs,
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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,nn,n,neqns;
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DP h,h2,halfh,x;
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int nv=y.size();
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Vec_DP ytemp(nv);
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h=htot/nstep;
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halfh=0.5*h;
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neqns=nv/2;
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for (i=0;i<neqns;i++) {
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n=neqns+i;
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ytemp[i]=y[i]+(ytemp[n]=h*(y[n]+halfh*d2y[i]));
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}
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x=xs+h;
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derivs(x,ytemp,yout);
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h2=h*h;
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for (nn=1;nn<nstep;nn++) {
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for (i=0;i<neqns;i++)
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ytemp[i] += (ytemp[neqns+i] += h2*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<neqns;i++) {
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n=neqns+i;
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yout[n]=ytemp[n]/h+halfh*yout[i];
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yout[i]=ytemp[i];
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}
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}
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