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/* -*-ePiX-*- */
#include "epix.h"
using namespace ePiX;
const int MAX(24);
const double x0(4);
const double ht(3); // camera height
const double INFTY(100000);
P f(double t)
{
return P(t, t*t, 0);
}
int main()
{
picture(P(-3,-3),P(3,3), "4x4in");
begin();
border();
set_crop();
viewpoint(0,-ht*ht, ht);
camera.look_at(P(0,0,1));
pen(Black(0.3), "0.1pt");
grid(P(-MAX,0), P(MAX, MAX*MAX), MAX, MAX*MAX/8);
grid(P(-MAX, 0, 2*ht), P(MAX, MAX*MAX, 2*ht), MAX, MAX*MAX/8);
pen(Blue(1.4));
envelope(f, -MAX/2, MAX/2, 20); // envelope of tangent lines
bbold(Blue());
Line(P(-100, INFTY, 0), P(100, INFTY, 0));
masklabel(P(0,0), P(0,2), "$(0,0)$", t);
label(P(0,INFTY), P(0,-2), "$(0,\\infty)$", b);
label(P(-0.25*INFTY,INFTY), P(0, 2), "Horizon", t);
masklabel(P(x0, x0*x0), P(-4,0), "$y=x^2$", l);
box(P(0,0));
box(P(0,INFTY));
pen(1);
plot(f, -MAX, MAX, 240);
camera.at(0,0,1000);
masklabel(P(0, ymin()), P(0,0),
"Projective equivalence of a parabola and a circle", t);
end();
}
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