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/*
* Copyright (c) 2003 CHABBERT Jean-Philippe
*
* This file is part of LORENE.
*
* LORENE is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2
* as published by the Free Software Foundation.
*
* LORENE is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with LORENE; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
*/
char _C[] = "$Header: /cvsroot/Lorene/Codes/Rot_star/Geodesics/rk4_exp.C,v 1.1 2003/02/07 17:31:52 jp_chabbert Exp $" ;
/*
* $Id: rk4_exp.C,v 1.1 2003/02/07 17:31:52 jp_chabbert Exp $
* $Log: rk4_exp.C,v $
* Revision 1.1 2003/02/07 17:31:52 jp_chabbert
* First version with rotstar input data
*
*
*
*
* $Header: /cvsroot/Lorene/Codes/Rot_star/Geodesics/rk4_exp.C,v 1.1 2003/02/07 17:31:52 jp_chabbert Exp $
*
*/
// C++ headers
// C headers
// Lorene headers
#include "etoile.h"
#include "nrutil.h"
#include "main.h"
void rk4(double y[], int n, double x, double h, double yout[]
, const Etoile_rot& star
, void (*derivs)(double, double [], double [] , const Etoile_rot&))
/*Given values for the variables y[1..n] and their derivatives dydx[1..n]
known at x, use the fourth-order Runge-Kutta method to advance the solution
over an interval h and return the incremented variables as yout[1..n], which
need not be a distinct array from y. The user supplies the routine
derivs(x,y,dydx), which returns derivatives dydx at x.*/
{
int i;
double xh,hh,h6,*dym,*dyt,*yt,*dydx;
dym=dvector(1,n);
dyt=dvector(1,n);
yt=dvector(1,n);
dydx=dvector(1,n);
hh=h*0.5;
h6=h/6.0;
xh=x+hh;
#ifdef DEBUG
printf("Entre dans rk4 ... ");
#endif
(*derivs)(x,y,dydx,star);
/* printf("expo: %f %f %f\n",x,y[1],dydx[1]); */
/* First step */
for (i=1;i<=n;i++) yt[i]=y[i]+hh*dydx[i];
/* Second step */
(*derivs)(xh,yt,dyt,star);
for (i=1;i<=n;i++) yt[i]=y[i]+hh*dyt[i];
/* Third step */
(*derivs)(xh,yt,dym,star);
for (i=1;i<=n;i++)
{
yt[i]=y[i]+h*dym[i];
dym[i] += dyt[i];
}
/* Fourth step */
(*derivs)(x+h,yt,dyt,star);
for (i=1;i<=n;i++) yout[i]=y[i]+h6*(dydx[i]+dyt[i]+2.0*dym[i]);
/* Free memory */
free_dvector(yt,1,n);
free_dvector(dyt,1,n);
free_dvector(dym,1,n);
free_dvector(dydx,1,n);
#ifdef DEBUG
printf("Fin de rk4\n");
#endif
}
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