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[WIP] Add Axes method for drawing infinite lines.#7506

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QuLogic wants to merge1 commit intomatplotlib:masterfromQuLogic:abline

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[WIP] Add Axes method for drawing infinite lines.#7506

QuLogic wants to merge1 commit intomatplotlib:masterfromQuLogic:abline

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QuLogic commentedNov 24, 2016

This is an implementation of an infinite line artist following the transforms I outlined in#5253. However, I did need to change fromax.dataLim toax.viewLim because the former is infinite when nothing else is on the plot. I'm not sure if that will cause problems (maybe in log-scaled plots?), though it seems to work:

importmatplotlib.pyplotaspltfig,ax=plt.subplots()ax.axline(linewidth=4,color='r')ax.axline(intercept=1)ax.axline(slope=5)ax.grid(True)ax.set_xlim(0,10)ax.set_ylim(0,10)plt.show()

https://youtu.be/DJjbFMoAw68

Unlikeaxhline andaxvline, there is no[xy]{min,max} or autoscaling based on these artists because I don't think it makes sense for infinite lines.

I've only implementedslope/intercept and not any of the alternates in#5253; not sure which ones we want to support. Also needs some tests, wrapper inpyplot, etc., so it's still WIP.

Add Axes method for drawing infinite lines.

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QuLogic added this to the2.1 (next point release) milestone

Nov 24, 2016

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QuLogic commentedNov 24, 2016

On a semilog plot, this is not correct, which can be seen by doing some interpolation:

The red line is not interpolated at all and is completely wrong; the dashed blue line is howax.plot works, which also uses no interpolation but keeps the right endpoints only; the green line is howaxline would work with a bit of extra points (instead of just 0,0->1,1). As can be seen in the figure, this requires a bit of finesse with the sampling as moving the view around will change the smoothness of the curve depending on how close it is to the asymptotes.

I guess it might be possible to tweak the sampling to get this right, though I don't want to spend too much time trying until we're sure what the intended API/effect is here.

loglog plots look okay since lines are still lines on them.

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dstansby commentedJan 31, 2017

This is pretty neat! Givenplot is technically broken on semi-log plots (as shown above), I think adding the currentaxline version that works on log-log and linear-linear would be fine.

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Jan 31, 2017

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This also needs a what's new entry, at least an image test, and some edge case tests too. (slope zero, negative slope, very large slope are the ones that come to my mind right now). Otherwise looks good!

lib/matplotlib/axes/_axes.py

		@@ -794,6 +794,69 @@ def axvline(self, x=0, ymin=0, ymax=1, **kwargs):
		return l

		@docstring.dedent_interpd
		def axline(self, slope=1, intercept=0, **kwargs):
		"""
		Add an infinite line across the axes.

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dstansbyJan 31, 2017

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'across an axis'?

lib/matplotlib/axes/_axes.py


		Parameters
		----------
		slope : scalar, optional, default: 1

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dstansbyJan 31, 2017

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Is there a reason this and intercept are optional? I would say the user should be forced to give them.

lib/matplotlib/axes/_axes.py

		See Also
		--------
		axhline : for strictly horizontal lines
		axvline : for strictly vertical lines

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dstansbyJan 31, 2017

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Do these get automatically linked? If not would be nice to have some sphinx markup to link to relevant methods.

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syrte commentedApr 21, 2017•
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A tentative suggestion on arguments, how about following forms:

def axline(a, b, *args, **kwargs):    """    a, b: scalar or tuple        Acceptable forms are        y0, b:            y = y0 + b * x        (x0, y0), b:            y = y0 + b * (x - x0)        (x0, y0), (x1, y1):            y = y0 + (y1 - y0) / (x1 - x0) * (x - x0)    ...

Accept following combinations: