added poormans contour example

svn path=/trunk/matplotlib/; revision=332

Author: jdh2358

CHANGELOG

@@ -1,5 +1,7 @@
 New entries should be added at the top
 
+2004-06-07 Fixed width/height issues for images - JDH
+
 2004-06-03 Fixed draw_if_interactive bug for semilogx; 
 
 2004-06-02 Fixed text clipping to clip to axes - JDH

examples/poormans_contour.py

@@ -0,0 +1,42 @@
+#!/usr/bin/env python
+"""
+Use a pcolor or imshow with a custom colormap to make a contour plot.
+A proper contour, with contour lines, is on the list of things to do
+"""
+
+from matplotlib.matlab import *
+
+
+def bivariate_normal(X, Y, sigmax=1.0, sigmay=1.0,
+                     mux=0.0, muy=0.0, sigmaxy=0.0):
+    """
+    Bivariate gaussan distribution for equal shape X, Y
+
+    http://mathworld.wolfram.com/BivariateNormalDistribution.html
+    """
+    Xmu = X-mux
+    Ymu = Y-muy
+
+    rho = sigmaxy/(sigmax*sigmay)
+    z = Xmu**2/sigmax**2 + Ymu**2/sigmay - 2*rho*Xmu*Ymu/(sigmax*sigmay)
+    return 1.0/(2*pi*sigmax*sigmay*(1-rho**2)) * exp( -z/(2*(1-rho**2)))
+
+
+delta = 0.01
+x = arange(-3.0, 3.0, delta)
+y = arange(-3.0, 3.0, delta)
+X,Y = meshgrid(x, y)
+Z1 = bivariate_normal(X, Y, 1.0, 1.0, 0.0, 0.0)
+Z2 = bivariate_normal(X, Y, 1.5, 0.5, 1, 1)
+
+
+cmap = ColormapJet(10)    # 10 discrete contours
+im = imshow(Z2-Z1, cmap)  # difference of Gaussians
+
+# set the interpolation method: 'nearest', 'bilinear', 'bicubic' and much more
+im.set_interpolation('bilinear')
+
+axis('off')
+#savefig('test')
+show()
+