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

/*
	solve	dx/dt = -2x + exp(-t)	x(0)=0
	
	analytic solution: x(t) = exp(-t) - exp(-2t)
*/

#define	NumVars		1

static void differential(int n, double x[], double t, double value[])
{
	value[0] = -2.00*x[0] + exp(-t);
}

main()
{
	int	kcnt;
	double	t, dt, tend;
	double	x[NumVars];
	char	*filename = "rkf-adp-t0.dat";
	FILE	*fd;
	
	if ((fd = fopen(filename,"w")) == NULL) {
		fprintf(stderr, "cannot open %s\n", filename);
		exit(1);
	}
	
	kcnt = 1000;
	dt = 1.00/2/2/2/2/2/2/2;
	tend = 10.00;
	
	/* initial values */
	t = 0.0;
	x[0] = 0.0;
	RungeKuttaFehlbergAdaptivefprint(fd, NumVars, x, t, dt);	// print initial values
	
	RungeKuttaFehlbergAdaptive(fd, NumVars, x, differential, &t, &dt, tend, kcnt);
	//RungeKuttaFehlbergAdaptive(fd, NumVars, x, differential, &t, &dt, kcnt/2);
	
	fclose(fd);
}