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sharun-s opened this issue Apr 26, 2019 · 3 comments · Fixed by #14424
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quiver(C=...) argument is not reasonably validated #14060

sharun-s opened this issue Apr 26, 2019 · 3 comments · Fixed by #14424
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API: argument checking Documentation status: confirmed bug
Milestone
v3.2.0

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@sharun-s
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sharun-s commented Apr 26, 2019 •
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Bug summary

Quiver plot issue matching key label color with arrow color

Code for reproduction

q=plt.quiver([1, 2,], [1, 1], [[49],[49]], [0],
   [[(0.6, 0.8, 0.5, 1.0 )],
    [(0.3, 0.1, 0.2, 1.0 )]],
       angles=[[45],[90]],
       )
plt.quiverkey(q, .5, .5, 7, r'vector2', labelcolor=(0.3, 0.1, .2, 1), labelpos='S', coordinates = 'figure')

Actual outcome

Figure_1

Expected outcome

The key label color and a vector are both set to (0.3, 0.1, .2, 1) but their colors are different.

Matplotlib version

  • Operating system: Ubuntu 18.04
  • Matplotlib version: 3.0.3
  • Matplotlib backend: TkAgg
  • Python version: 3.6
  • Jupyter version (if applicable):
  • Other libraries:

pip3 install matplotlib
@timhoffm
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This is actually not an issue with quiverkey(labelcolor=...), as can be checked by setting the label color to 'red'. (0.3, 0.1, .2, 1) is a dark violet, and that's what the label color is.

The problem is that the C argument is not doing, what one might expect:

In [[(0.6, 0.8, 0.5, 1.0 )], [(0.3, 0.1, 0.2, 1.0 )]] the first two numbers 0.6, 0.8 are used to lookup the colors of the two arrows from the colormap (whose norm is in some way determined by all the numbers - didn't check exactly).

This is not a reasonable behavior - either we should raise an error with these inputs or support explicit colors in C. Either way the documentation must be improved as well.

@timhoffm timhoffm changed the title Matching Quiverkey label color with arrow color quiver(C=...) argument is not reasonably validated Apr 27, 2019
@ImportanceOfBeingErnest
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xref https://stackoverflow.com/questions/55871552/matplotlib-quiver-plot-matching-key-label-color-with-arrow-color/

I think this is above all a documentation issue. It currently says for C

C : 1D or 2D array, sequence, optional
The arrow colors

and for color

color : [ color | color sequence ], optional
This is a synonym for the PolyCollection facecolor kwarg. If C has been set, color has no effect.

@anntzer
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anntzer commented Apr 28, 2019

Looks like a duplicate/variant of #13423, perhaps?

@timhoffm timhoffm mentioned this issue Apr 29, 2019
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efiring added a commit to efiring/matplotlib that referenced this issue Jun 2, 2019
@efiring
ENH: Add argument size validation to quiver.
ff923bc 
Closes matplotlib#14060.
@efiring efiring mentioned this issue Jun 2, 2019
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ImportanceOfBeingErnest pushed a commit that referenced this issue Aug 30, 2019
@efiring @ImportanceOfBeingErnest
ENH: Add argument size validation to quiver. (#14424)
e9677c1 
Closes #14060.
@QuLogic QuLogic added this to the v3.2.0 milestone Aug 31, 2019
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Labels
API: argument checking Documentation status: confirmed bug
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ENH: Add argument size validation to quiver. efiring/matplotlib
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@QuLogic @anntzer @timhoffm @sharun-s @ImportanceOfBeingErnest