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#!/usr/bin/env python
import sys;sys.path.insert(0, "..")
from math import *
#sys.path.insert(0, os.path.expanduser("~/python/pyx-trunk"))
from pyx import *
# File for invalid parametrisations of Bezier curves
# Some examples
def Dx_m(Dy):
return (-1-2*Dy-sqrt((1+2*Dy)**2+3))/3.0
def Dx_p(Dy):
return (-1-2*Dy+sqrt((1+2*Dy)**2+3))/3.0
def pass00(Dy):
return 1.0/(3.0*(Dy+1))
def pass10(Dy):
return (1.0+Dy**3)/(3.0*(Dy+1))
def acurve(Dx, Dy, trafo_reverse=False):
p = path.curve(0,0, 0,1, Dx,1+Dy, 1,0)
if trafo_reverse:
# calculate the trafo to put p2=(1,-1):
# (for the right branch only)
x2, y2 = Dx, Dy+1
tr1 = trafo.scale(1, -1.0/y2)
pp = tr1.apply_pt(x2, y2)
tr2 = trafo.trafo(matrix=((1, (pp[0]-1)), (0, 1)))
p = p.transformed(tr2*tr1)
c = canvas.canvas()
c.stroke(p, [deco.shownormpath()])
#c.text(-0.2, -10*unit.x_pt, r"\noindent$\Delta x=%g $\par\noindent$\Delta y=%g$"%(Dx,Dy),
# [text.parbox(4), text.size.footnotesize])
return c
dx = 3
dy = -3
Dy = -2.5
e = 0.1
# test the left branch:
cc = acurve(pass00(Dy), Dy) # passes through startpoint
#cc = acurve(Dx_m(Dy)-e, Dy)
c = acurve(Dx_m(Dy) , Dy); cc.insert(c, [trafo.translate(1*dx, 0)])
c = acurve(Dx_m(Dy)+e, Dy); cc.insert(c, [trafo.translate(2*dx, 0)])
# test the right branch:
#cc = acurve(Dx_p(Dy)-e, Dy, True)
#c = acurve(Dx_p(Dy) , Dy, True); cc.insert(c, [trafo.translate(1*dx, 0)])
##c = acurve(Dx_p(Dy)+e, Dy, True); cc.insert(c, [trafo.translate(2*dx, 0)])
#c = acurve(pass10(Dy), Dy, True); cc.insert(c, [trafo.translate(2*dx, 0)]) # passes through endpoint
cc.writePDFfile()
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