cleanup patch with contourf change

John, Jeff,

The attached patch for includes several minor cleanups plus one change of substance--it may require a slight change in some invocations of contourf. The change is in the handling of contour levels for contourf.

Old version: a list of levels as one of the positional arguments specified the lower bound of each filled region; the upper bound of the last region was taken as a very large number. Hence, it was not possible to specify that z values between 0 and 1, for example, be filled, and that values outside that range remain unfilled.

New version: a list of N levels is taken as specifying the boundaries of N-1 z ranges. Now the user has more control over what is colored and what is not. Repeated calls to contourf (with different colormaps or color specifications, for example) can be used to color different ranges of z. Values of z outside an expected range are left uncolored.

Old: contourf(z, [0, 1, 2]) would yield 3 regions: 0-1, 1-2, and >2.
New: it would yield 2 regions: 0-1, 1-2. If the same 3 regions were desired, the equivalent list of levels would be [0, 1, 2, 1e38].

Color mapping is still based on the lower limits of the regions.

Eric (7.49 KB)