#include <stdio.h>
#include <math.h>
/* runge2m.c : 1999 3 28 by T.Oguni */
#define M 2
#define NF 200
double an[M];
main(){
  double x[M],u[NF+1],v[NF+1];
  double h=0.1;
  int n0=0, nf=200, m=2, i;
  x[0]=0.0; x[1]=0.25;
  runge2(h,x,u,v,n0,nf,m);
  printf("u and v\n");
  for (i=n0; i<nf+1; i+=50){
    printf("%d %f %f\n", i, u[i], v[i]);}
}
/* function */
func(x)
double x[M];
{
  an[0]=x[0]*(1.0-x[1]*x[1])-x[1];
  an[1]=x[0];
  return;
}
/* function */
runge2(h,x,u,v,n0,nf,m)
double h, x[M], u[NF+1], v[NF+1];
int n0, nf, m;
{
  double y[M],k1[M],k2[M];
  int n, i;
  n=n0;
  while (n<=nf){
    func(x);
    for (i=0; i<m; i++){
      k1[i]=h*an[i]; y[i]=x[i]+k1[i]; }
    func(y);
    for (i=0; i<m; i++){
      k2[i]=h*an[i]; x[i]=x[i]+(k2[i]+k1[i])/2.0; }
    u[n]=x[1]; v[n]=x[0]; n++;
  }
  return;
}