File:Gravity well plot.svg

import graph3;
settings.render=0;

typedef real fun(real);

fun Phi(real R, real GM_R, real shift=0) {
  return new real(real r) {
    real r_R = abs(r) / R;
    if (r_R >= 1)
      return -GM_R / r_R + shift;
    else
      return 0.5 GM_R * (r_R^2 - 3) + shift;
  };
}

typedef real fun2(pair);
fun2 revolve(fun f) {return new real(pair z) {return f(abs(z));};}

picture pic;

size3(pic,300,0);
size(pic.xsize3,pic.ysize3);

currentprojection=perspective(0,20,4);

draw(pic,surface(revolve(Phi(2,7)),(-12,-12),(12,12),nx=20,Spline),lightgray,meshpen=black+thick(),nolight);

attach(pic.fit());

draw(shift(0,6)*graph(Phi(2,7,-10),-12,12));