#include <stdio.h>
#include <math.h>
#include "RK.h"

/*
	d x0 / dt = (a^2 - x0^2 - x1^2) x0 - x1
	d x1 / dt = (a^2 - x0^2 - x1^2) x1 + x0
*/

#define	NumVars		2

#define Radius	2.5
static void differential(int n, double x[], double t, double value[])
{
  value[0] = ( Radius*Radius - x[0]*x[0] - x[1]*x[1] ) * x[0] - x[1];
  value[1] = ( Radius*Radius - x[0]*x[0] - x[1]*x[1] ) * x[1] + x[0];
}

main()
{
  int		kcnt;
  double	t, dt, tend;
  double	x[NumVars];
  char		*filename = "rkf-adp-t3.dat";
  FILE		*fd;
  
  if ((fd = fopen(filename,"w")) == NULL) {
    fprintf(stderr, "cannot open %s\n", filename);
    exit(1);
  }
  
  kcnt = 50000;
  dt = 0.0001;
  tend = 100.00;
  
  /* initial values */
  t = 0.0;
  x[0] = 3.0;
  x[1] = 5.0;
  
  RungeKuttaFehlbergAdaptivefprint(fd, NumVars, x, t, dt);	// print initial values
  RungeKuttaFehlbergAdaptive(fd, NumVars, x, differential, &t, &dt, tend, kcnt);
  
  fclose(fd);
}