gallery/graphs/integral.py

   1 from pyx import *
   2
   3 a, b = 2, 9 # integral area
   4
   5 p = graph.axis.painter.regular(basepathattrs=[deco.earrow.normal],
   6                                titlepos=0.98, titledirection=None)
   7 ticks = [graph.axis.tick.tick(a, label="$a$"),
   8          graph.axis.tick.tick(b, label="$b$")]
   9 g = graph.graphxy(width=8, x2=None, y2=None,
  10                   x=graph.axis.linear(title="$x$", min=0, max=10,
  11                                       manualticks=ticks,
  12                                       parter=None, painter=p),
  13                   y=graph.axis.linear(title="$y$", parter=None, painter=p))
  14 d = g.plot(graph.data.function("y(x)=(x-3)*(x-5)*(x-7)"))
  15 g.finish()
  16 p = d.path # the path is available after the graph is finished
  17
  18 pa = g.xgridpath(a)
  19 pb = g.xgridpath(b)
  20 (splita,), (splitpa,) = p.intersect(pa)
  21 (splitb,), (splitpb,) = p.intersect(pb)
  22 area = (pa.split([splitpa])[0] <<
  23         p.split([splita, splitb])[1] <<
  24         pb.split([splitpb])[0].reversed())
  25 area[-1].close()
  26 g.stroke(area, [deco.filled([color.gray(0.8)])])
  27 g.text(g.pos(0.5 * (a + b), 0)[0], 1,
  28        r"\int_a^b f(x){\rm d}x", [text.halign.center, text.mathmode])
  29 g.writeEPSfile("integral")
  30 g.writePDFfile("integral")