Re: [matplotlib-devel] Bugs and patches posted

[John H. <jdh...@ac...>]

>>>>> "Zachary" == Zachary Pincus <zp...@st...> writes:

    Zachary> Hello - I just posted a few bugs (and patches to fix
    Zachary> them) to the sourceforge bugtracker page before I
    Zachary> realized that the email list is preferred.

More people see the list I think, but the SF mirror for the dev list
is generally woefully out of date, so it's a tossup.

    Zachary> Short story: I found and (hopefully) fixed a problem with
    Zachary> pcolor on non-square arrays, a startup error in the
    Zachary> interactive.py shell, and a problem with repeated output
    Zachary> when saving postscript backend figures. The details of
    Zachary> the bugs and patches are copied below.

Thanks for the detailed information and patches!

    Zachary> This happens because the shape of the X and Y arrays (the
    Zachary> output of a meshgrid call on line 1782) have the wrong
    Zachary> shape. In particular, the shape is backward.  e.g. if
    Zachary> C.shape = (x,y), then X.shape = Y.shape = (y, x).

The behavior of meshgrid certainly is a bit counter-intuitive.  Eg, in
matlab

    >> x = [1:7];
    >> y = [1:5];
    >> [X,Y] = meshgrid(x,y);
    >> Z = rand(length(x), length(y));
    >> pcolor(X,Y,Z);
    ??? Error using ==> surface
    Matrix dimensions must agree.

matplotlib fails in the same way.  I've updated the docs in meshgrid,
pcolor and fixed the meshgrid call in the case of pcolor(Z) for
nonsquare Z.

I added the following to the pcolor docs - let me know if you agree
with this.

"""
    Note, the behavior of meshgrid in matlab is a bit
    counterintuitive for x and y arrays.  For example,

      x = arange(7)
      y = arange(5)
      X, Y = meshgrid(x,y)

      Z = rand( len(x), len(y))
      pcolor(X, Y, Z)

    will fail in matlab and matplotlib.  You will probably be
    happy with

      pcolor(X, Y, transpose(Z))

    Likewise, for nonsquare Z,

      pcolor(transpose(Z))

    will make the x and y axes in the plot agree with the numrows
    and numcols of Z
"""

    Zachary> Patch: Change matplotlib/axes.py line 1782 from: X, Y =
    Zachary> meshgrid(range(numRows), range(numCols)) to: X, Y =
    Zachary> meshgrid(range(numCols), range(numRows))

Done

    Zachary> (*)
    Zachary> http://matplotlib.sourceforge.net/matplotlib.mlab.html#-meshgrid

Fixed doc bug.


    Zachary> Patch: Insert the command: interpreter.feed("from
    Zachary> matplotlib.backends.backend_gtk import ShowOn") somewhere
    Zachary> before line 206.

Fixed -- I don't know how this got removed.

    Zachary> Patch: Insert the following lines at the end of the
    Zachary> print_figure method of the FigurePS class in the file
    Zachary> matplotlib/ backends/backend_ps.py (line 189):
    Zachary> self._pswriter = StringIO()
    Zachary> self._pswriter.write(_psHeader)

Added a flush method, called by __init__ and after writing the figure.

Thanks again -- that was very helpful.

John Hunter