rk4.h

#ifndef RK4_H
#define RK4_H
double rk4(double xi, double yi, double h, double df()) {
	double k[4];
	k[0] = df(xi, yi);
	k[1] = df(xi + h/2, yi + h*k[0])/2;
	k[2] = df(xi + h/2, yi + h*k[1])/2;
	k[3] = df(xi + h, yi + h*k[2]);
	return yi + h(k[0]+2*(k[1]+k[2]) + k[3])/6;
}
#endif