[ENH]: contour kwarg for negative_linestyle #23028

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1. jklymak

   added

   New feature

   API: consistencyConsistency of the matplotlib API, including naming, behavior, defaults, …Consistency of the matplotlib API, including naming, behavior, defaults, …

   API: default changesChanges to default behaviorChanges to default behavior

   and removed

   New feature

   on May 9, 2022
2. andrew-fennell commented on May 13, 2022

   

   andrew-fennell

   on May 13, 2022

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   Should the current linestyles kwarg be used to accomplish this or should a new kwarg be added? I have a simple solution adding a new kwarg (though it would need a little more work before it is ready).

   The following code snippet and images will show a solution with an added kwarg, but I expect this is not exactly what you had in mind.

   import numpy as np
   import matplotlib.pyplot as plt
   
   delta = 0.025
   x = np.arange(-3.0, 3.0, delta)
   y = np.arange(-2.0, 2.0, delta)
   X, Y = np.meshgrid(x, y)
   Z1 = np.exp(-X**2 - Y**2)
   Z2 = np.exp(-(X - 1)**2 - (Y - 1)**2)
   Z = (Z1 - Z2) * 2
   
   # Negative contour defaults to dashed
   fig, ax = plt.subplots()
   CS = ax.contour(X, Y, Z, 6, colors='k')
   ax.clabel(CS, fontsize=9, inline=True)
   ax.set_title('Single color - negative contours dashed (default)')
   
   # Set negative contours to be solid instead of dashed (default)
   # using negative_linestyle='solid'
   fig2, ax2 = plt.subplots()
   CS = ax2.contour(X, Y, Z, 6, colors='k', negative_linestyles='solid')
   ax2.clabel(CS, fontsize=9, inline=True)
   ax2.set_title('Single color - negative contours solid')
   

   Default

   

   negative_linestyles='solid'

   
3. timhoffm commented on May 13, 2022

   

   timhoffm

   on May 13, 2022

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   Should the current linestyles kwarg be used to accomplish this or should a new kwarg be added?

   How would we squeeze this into the current linestyles parameter? The only thing I could imagine is something like linestyles={'positive': 'solid', 'negative': 'dotted'}, which I find a bit cumbersome. I suppose an extra kwarg is simpler.
4. andrew-fennell commented on May 13, 2022

   

   andrew-fennell

   on May 13, 2022

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   How would we squeeze this into the current linestyles parameter?

   I had no good solution for this either, but thought I would ask just in case.

   The next question is:

   1. should this be a boolean (the rcParams method seems to be)
   2. or should the kwarg accept a separate entry for negative linestyles?

   I think the latter makes a lot more sense, but I don't work with contour plots regularly.
5. jklymak commented on May 13, 2022

   

   jklymak

   on May 13, 2022

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   I think since the rcParam is separate, its fine to keep the (potential) kwarg separate. BTW I'm not wedded to this idea, but it does seem strange to have a feature only accessible by rcParam.

   As for bool vs string, I'd say both? right now the rcParam defaults to "dashed" - I think that's fine for a kwarg as well, but being able to say False to skip the behaviour would be nice as well.
6. andrew-fennell commented on May 13, 2022

   

   andrew-fennell

   on May 13, 2022

   Contributor

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   BTW I'm not wedded to this idea

   I can mock-up a basic solution. Maybe we can get opinions from other contributors and maintainers in the meantime.

   I think this would add value because it would make customization of negative contours more straightforward. Since this doesn't require removing any current functionality, I don't see any cons to adding the kwarg.

   👍React with 👍3Reacted by Jody Klymak, Tim Hoffmann and Oscar Gustafsson
7. tacaswell

   closed this as completedin #23266on Jun 24, 2022
8. QuLogic

   added this to the v3.6.0 milestone on Jun 25, 2022