[genius] Tue Sep 09 10:08:38 2014 Jiri (George) Lebl <jirka 5z com>

[George Lebl <jirka src gnome org>]

commit c1d3101f1092464476d39e5f0e8a26b39a3b5b27
Author: Jiri (George) Lebl <jiri lebl gmail com>
Date:   Fri Sep 12 11:14:04 2014 -0500

    Tue Sep 09 10:08:38 2014  Jiri (George) Lebl <jirka 5z com>
    
        * src/graphing.c: fixes in help/error texts.  Thanks to Marek
          Černocký

 examples/peano.gel |   31 +++++++++++++++++++++++++++++++
 1 files changed, 31 insertions(+), 0 deletions(-)
---
diff --git a/examples/peano.gel b/examples/peano.gel
new file mode 100644
index 0000000..0210b4a
--- /dev/null
+++ b/examples/peano.gel
@@ -0,0 +1,31 @@
+# Category: Calculus
+# Name: Peano surface (using polar coordinates)
+#
+# The Peano surface drawn using polar coordinates.
+#
+# z = (y-x^2)(2x^2-y)
+#
+# The function giving the surface has a maximum on every line through the origin,
+# but the origin is not an extremum of the function.  Note that second derivative
+# test fails on the line y=0, even though along that line the function still has
+# a maximum.  While the function has a maximum along every line, it has a minimum
+# along a curve y=ax^2 for any 1 < a < 2.
+#
+# The properties of the function can be easily seen from the factorization and seeing
+# the regions where each factor is positive or negative.
+
+data = null;
+for r=0 to 0.25 by 0.02 do (
+  for theta=0 to 2*pi by pi/15 do (
+    x = r*cos(theta);
+    y = r*sin(theta);
+    data = [data;[x,y,3*x^2*y-y^2-2*x^4]]
+  )
+);
+
+SurfacePlotDrawLegends = false; # don't draw the legend
+PlotWindowPresent(); # Make sure the window is raised
+
+# Plot the data
+SurfacePlotData(data);
+