// This does the 3 body 3-4-5 configuration.
// This version is the simplest.
// This version updates x too often.
#include <stdio.h>
#include <math.h>
static double s(double x){return x*x;}
typedef struct {double x, y, xd, yd, m, mid;} pt;
//  xd & yd include factor dt. mid is dt^2/mass.

int main(){
  pt z[] = {{0,4,0,0,3,0},{3,0,0,0,4,0},{0,0,0,0,5,0}};
  double dt = .000001;
  double t = 0;
  void pr(char * m){int k;
     printf("t=%12.7f %s\n", t, m);
      for(k=0; k<3; ++k) {pt*p = z+k;
     printf("%10.7f %10.7f %10.7f %10.7f\n",
            p->x, p->y, p->xd/dt, p->yd/dt);}
    }
  void conf(pt* j, pt* k){
   double dx = j->x - k->x, dy = j->y - k->y, s2 = s(dx) + s(dy);
   double d = j->m*k->m/(sqrt(s2)*s2);
   double fx = dx*d, fy = dy*d;
   j->xd -= fx*j->mid; j->yd -= fy*j->mid;
   k->xd += fx*k->mid; k->yd += fy*k->mid;
   j->x += j->xd; j->y += j->yd;
   k->x += k->xd; k->y += k->yd;
   }
   void step(){conf(z,z+1); conf(z,z+2); conf(z+1,z+2); t += dt;}
   {int j=3; while(j--) z[j].mid = s(dt)/z[j].m;}
   pr("init"); step(); pr("once");
   while(1){int j = 9999999; while(j--) step(); pr("Chug");}
  }