#### 7.37 bug in contourplot in Maple 6 (15.4.00)

It seems that maple6 (trial version) cannot calculate contours correctly.

Try the phase space plot for the simple pendulum (m=l=1, g=10):

Tkin:=omega^2/2;
Upot:=10*(1-cos(phi));
plots[contourplot](Tkin+Upot,phi=-3*Pi/2..3*Pi/2,omega=-10..10,
contours=[1,5,9,13,17,21,25,29]);

In version 5.01 we observe correctly that beyond the 5th contour we have rotations (rather
than oscillations) as solutions. In Maple6 all 8 contours are (wrongly) shown as
closed.

It is corrected with Maple 6.01. (U. Klein)

For a more dramatic example of this bug, try

plots[contourplot](y/x,x=0.1 .. 1, y = 0.1 .. 1);

This bug aﬀects the contourplot of any expression f where denom(f) is not 1. What is
returned is a contourplot of numer(f), not f.

The culprit is in line 133 of ``plot/iplot2d``

:

f := `plot3d/makefunc`(numer(F),[x, y])

It can be ﬁxed by replacing numer(F) by F in that line.