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/* -*-ePiX-*- */
/* shadeplot.xp -- February 09, 2003 */
#include "epix.h"
using namespace ePiX;
double k=4; // change width of hump
double dx = 0.05; // width of thin shaded region
double x = 1/sqrt(k); // position of thin shaded region
double dy = 0.25; // for vertical distance between labels; kludgey
double f(double t) { return sqrt(fabs(k)/(2*M_PI))*exp(-k*t*t); }
P pt1 = P(x, f(x)+2*dy), pt2 = P(x+dx,f(x)+dy), pt3 = P(x+3*dx,f(x));
int main()
{
unitlength("1pt");
picture(150, 150);
bounding_box(P(0,0), P(1,1));
offset(120, -320);
begin();
fill();
gray(0.1); shadeplot(f, x_min, x, 90);
gray(0.4); rect(P(x,f(x)), P(x+dx, 0));
gray(0.6); shadeplot(f, x, x+dx, 10);
fill(false);
arrow_camber(0.25); arrow_fill(1);
arrow(pt1, P(0.5*(x_min+x), 0.5*f(0.5*(x_min+x))),
P(0,0), "$F(x)=\\displaystyle\\int_a^x f(t)\\,dt$", tr);
arrow(pt2, P(x+0.5*dx, f(x)),
P(0,0), "Area of rectangle = $f(x)\\,dx$", tr);
arrow(pt3, P(x+dx, 0.5*f(x+dx)),
P(0,0), "Area = $F(x+dx)-F(x)$", tr);
bold();
plot(f, x_min, x_max, 120);
plain(); h_axis(4); v_axis(4);
label(P(x_min,0), P(0,-5), "$a$", b);
label(P(x,0), P(0,-5), "$x$", b);
label(P(x+dx,0), P(0,-2), "$x+dx$", br);
end();
}
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