/* -*-ePiX-*- */
#include "epix.h"
using namespace ePiX;

double ma(2), mb(1.5), mc(sqrt((ma - mb)*(ma + mb))), mt(M_PI_2), dt(0.3);

P f(double t)
{
  return P(ma*Cos(t), mb*Sin(t));
}

void Arrow(const P& tail, const P& head, double t = 0.5)
{
  P tmp(tail + t*(head - tail));
  line(tmp, head);
  arrow(tail, tmp);
}

int main()
{
  picture(P(-ma,-mb), P(ma,mb), "2 x 1.5in");

  begin();
  arrow_width(6);
  arrow_ratio(2);
  arrow_inset(0.75);

  P Sun(-mc, 0), pP(f(mt)), pV(f(mt + 0.001));

  bold();
  plot(f, 0, 2*M_PI, 120);

  spot(Sun, P(0, -4), "\\textsf{\\itshape Sun}", b);
  spot(pP, P(0, 4), "\\textsf{\\itshape Planet}", tr);

  Arrow(pP, Sun, 0.4);
  arrow(f(mt + dt), f(mt + dt + 0.001));

  label(0.5*(pP + Sun), P(2, -2), "\\textsf{\\itshape Force}", br);

  tikz_format();
  end();
}