55 lines
1.4 KiB
C++
55 lines
1.4 KiB
C++
#include <cmath>
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#include "nr.h"
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using namespace std;
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extern DP dxsav;
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extern int kmax,kount;
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extern Vec_DP *xp_p;
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extern Mat_DP *yp_p;
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void NR::odeint(Vec_IO_DP &ystart, const DP x1, const DP x2, const DP eps,
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const DP h1, const DP hmin, int &nok, int &nbad,
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void derivs(const DP, Vec_I_DP &, Vec_O_DP &),
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void rkqs(Vec_IO_DP &, Vec_IO_DP &, DP &, const DP, const DP,
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Vec_I_DP &, DP &, DP &, void (*)(const DP, Vec_I_DP &, Vec_O_DP &)))
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{
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const int MAXSTP=10000;
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const DP TINY=1.0e-30;
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int i,nstp;
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DP xsav,x,hnext,hdid,h;
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int nvar=ystart.size();
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Vec_DP yscal(nvar),y(nvar),dydx(nvar);
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Vec_DP &xp=*xp_p;
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Mat_DP &yp=*yp_p;
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x=x1;
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h=SIGN(h1,x2-x1);
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nok = nbad = kount = 0;
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for (i=0;i<nvar;i++) y[i]=ystart[i];
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if (kmax > 0) xsav=x-dxsav*2.0;
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for (nstp=0;nstp<MAXSTP;nstp++) {
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derivs(x,y,dydx);
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for (i=0;i<nvar;i++)
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yscal[i]=fabs(y[i])+fabs(dydx[i]*h)+TINY;
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if (kmax > 0 && kount < kmax-1 && fabs(x-xsav) > fabs(dxsav)) {
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for (i=0;i<nvar;i++) yp[i][kount]=y[i];
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xp[kount++]=x;
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xsav=x;
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}
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if ((x+h-x2)*(x+h-x1) > 0.0) h=x2-x;
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rkqs(y,dydx,x,h,eps,yscal,hdid,hnext,derivs);
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if (hdid == h) ++nok; else ++nbad;
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if ((x-x2)*(x2-x1) >= 0.0) {
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for (i=0;i<nvar;i++) ystart[i]=y[i];
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if (kmax != 0) {
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for (i=0;i<nvar;i++) yp[i][kount]=y[i];
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xp[kount++]=x;
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}
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return;
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}
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if (fabs(hnext) <= hmin) nrerror("Step size too small in odeint");
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h=hnext;
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}
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nrerror("Too many steps in routine odeint");
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}
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