legends on plots

[tvn]

Hi, I try to add legend on a plot (created below) but doesn't seem to have any success.  There was no error, the legends just won't show up.

var('x y')

xrange = (x,0,5)

yrange = (y,0,5)

f1 = implicit_plot(x**2-4*x+y**2==0,xrange,yrange,color='red',linewidth=5,legend_label='x^2 - 4x + y^2 == 0') 

f2 = implicit_plot(x*y==1,xrange,yrange,linewidth=5,legend_label='x*y==1')

result = f1+f2

result.legend(True)

result.show(legend_loc='upper right',frame=True)

[Liam Dalton]

I have similar issues when running your code. However, the same code works if you do not do implicit plotting:

var('x y')

xrange = (x,0,5)

yrange = (y,0,5)

f1 = plot(x**2,xrange,color='red',legend_label='x^2 - 4x + y^2 == 0') 

f2 = plot(x,xrange,legend_label='x*y==1')

result = f1+f2

result.legend(True)

result.show(legend_loc='upper right',frame=True)

To me this implies that the problem is with implicit plotting.

[kcrisman]

On Thursday, March 6, 2014 2:24:00 PM UTC-5, Liam Dalton wrote:

I have similar issues when running your code. However, the same code works if you do not do implicit plotting:

var('x y')

xrange = (x,0,5)

yrange = (y,0,5)

f1 = plot(x**2,xrange,color='red',legend_label='x^2 - 4x + y^2 == 0') 

f2 = plot(x,xrange,legend_label='x*y==1')

result = f1+f2

result.legend(True)

result.show(legend_loc='upper right',frame=True)

To me this implies that the problem is with implicit plotting.

Correct - I've been playing with this for the past few minutes, and contour plots (of which implicit plots are a subset) simply don't do this, even though there is code in the ContourPlot class to handle legends!  http://git.sagemath.org/sage.git/tree/src/sage/plot/contour_plot.py#n191 for implicit plot situation.

var('x y')

P = contour_plot(x^2+y^2==1,(x,-1,1),(y,-1,1),plot_points=150, contours=(0,0), fill=False, cmap=["blue"],legend_label='test')

print P.legend()

P.legend(True)

print P.legend()

print P[0].options()['legend_label']

show(P)

shows this.  Not only this, but the legend is inexplicably not set to True.

I have a feeling that we need to do what we do in plot/disk.py or something; my guess (only a guess) is that the matplotlib thing that does contour plots (contour) only accepts labels directly for the individual contours, which is http://matplotlib.org/api/pyplot_api.html#matplotlib.pyplot.clabel

In fact, http://matplotlib.org/api/pyplot_api.html#matplotlib.pyplot.contour seems to confirm that we shouldn't be trying to label contour plots with legends. (Which makes sense, since they have their own labeling mechanism).  However, for implicit plots, this might cause a problem.  A workaround like at the bottom of 

http://matplotlib.org/examples/pylab_examples/contourf_hatching.html

might work.

[kcrisman]

This is now http://trac.sagemath.org/ticket/15903

[ThanhVu (Vu) Nguyen]

legend would work on plot but I can't run my code on plot  (it won't take the variable y)  

plot(x**2-4*x+y**2==0,xrange,yrange,color='red',linewidth=5,legend_label='x^2 - 4x + y^2 == 0')

Traceback (click to the left of this block for traceback)
...
ValueError: free variable: y

Vu, 

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