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plt.pcolormesh shape mismatch when shading='gouraud' #8422

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#31362
#26320
Open
plt.pcolormesh shape mismatch when shading='gouraud'#8422
#31362
#26320
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Difficulty: Mediumhttps://matplotlib.org/devdocs/devel/contribute.html#good-first-issuesGood first issueOpen a pull request against these issues if there are no active ones!keepItems to be ignored by the “Stale” Github Actiontopic: pcolor/pcolormesh
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@egranstedt

Description

@egranstedt
egranstedt
opened on Apr 3, 2017

Bug report

Bug summary

When running plt.pcolormesh(X, Y, C, shading='flat'), if C.shape == (nrows, ncols), then if X and Y are 2-D arrays, their shapes must be either (nrows, ncols) or (nrows+1, ncols+1). If shading='gouraud', however, the latter results in an error. The code snippet below uses 1-D arrays for X and Y, but the same error occurs when they are the equivalent 2-D arrays.

Code for reproduction

import numpy as np
import matplotlib.pyplot as plt
x = np.arange(-4, 5)
y = np.arange(-6, 7)
xe = np.linspace(-4.5, 4.5, 10)
ye = np.linspace(-6.5, 6.5, 14)
c = np.exp(-0.5*0.125*(x.reshape(1, -1)**2 + y.reshape(-1, 1)**2))
plt.pcolormesh(xe, ye, c, shading='flat')  # works
plt.pcolormesh(x, y, c, shading='gouraud')  # works
plt.pcolormesh(xe, ye, c, shading='gouraud')  # doesn't work

Actual outcome

Traceback (most recent call last):

  File "<ipython-input-67-154f761638cd>", line 1, in <module>
    plt.pcolormesh(xe, ye, c, shading='gouraud')

  File "/home/egranstedt/anaconda3/lib/python3.6/site-packages/matplotlib/pyplot.py", line 3245, in pcolormesh
    ret = ax.pcolormesh(*args, **kwargs)

  File "/home/egranstedt/anaconda3/lib/python3.6/site-packages/matplotlib/__init__.py", line 1892, in inner
    return func(ax, *args, **kwargs)

  File "/home/egranstedt/anaconda3/lib/python3.6/site-packages/matplotlib/axes/_axes.py", line 5569, in pcolormesh
    X, Y, C = self._pcolorargs('pcolormesh', *args, allmatch=allmatch)

  File "/home/egranstedt/anaconda3/lib/python3.6/site-packages/matplotlib/axes/_axes.py", line 5187, in _pcolorargs
    C.shape, Nx, Ny, funcname))

TypeError: Dimensions of C (13, 9) are incompatible with X (10) and/or Y (14); see help(pcolormesh)

Expected outcome

I expected pcolormesh would accept the same arrays for X and Y irrespective of the setting of the shading` keyword argument.

Matplotlib version

  • The error occurs with Matplotlib version 2.0.0 in the python 3.6 interpreter on Linux (installed via anaconda), but also seems to exist in older versions of Matplotlib (e.g., 1.5.1)

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    Difficulty: Mediumhttps://matplotlib.org/devdocs/devel/contribute.html#good-first-issuesGood first issueOpen a pull request against these issues if there are no active ones!keepItems to be ignored by the “Stale” Github Actiontopic: pcolor/pcolormesh

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