#define NRANSI#include "nrutil.h"void rk4(float y[], float dydx[], int n, float x, float h, float yout[],	void (*derivs)(float, float [], float [])){	int i;	float xh,hh,h6,*dym,*dyt,*yt;	dym=vector(1,n);	dyt=vector(1,n);	yt=vector(1,n);	hh=h*0.5;	h6=h/6.0;	xh=x+hh;	for (i=1;i<=n;i++) yt[i]=y[i]+hh*dydx[i];	(*derivs)(xh,yt,dyt);	for (i=1;i<=n;i++) yt[i]=y[i]+hh*dyt[i];	(*derivs)(xh,yt,dym);	for (i=1;i<=n;i++) {		yt[i]=y[i]+h*dym[i];		dym[i] += dyt[i];	}	(*derivs)(x+h,yt,dyt);	for (i=1;i<=n;i++)		yout[i]=y[i]+h6*(dydx[i]+dyt[i]+2.0*dym[i]);	free_vector(yt,1,n);	free_vector(dyt,1,n);	free_vector(dym,1,n);}#undef NRANSI