nx.draw and plt.Circle

[vjktmail]

I'd like to overlay a circle on a graph drawn by nx.draw(). E.g., a circle around a specific node.

I tried:

nx.draw(...)

plt.Circle(...)

plt.show()

But the circle does not appear.  Note I used one of the pos values that nx.draw(..) was given for the circle center.

Is this possible?  What am I doing wrong?

[Daniel Schult]

Can you create a <10 line example that doesn't work?

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[vjktmail]

Hi Daniel,

I forgot to mention I tried it in IPython.  Here is an example:

import networkx as nx

gsize = 4 #square grid size

gg=nx.generators.grid_2d_graph(gsize,gsize) #grid graph gg

posg = nx.layout.fruchterman_reingold_layout(gg)

nx.draw(gg,posg)

center = posg[(0,0)]

plt.Circle(center, radius=5)

plt.show()

[vjktmail]

I meant to say I used IPython Notebook.

[Aric Hagberg]

Try
import matplotlib.pyplot as plt

import networkx as nx
gsize = 4 #square grid size
gg=nx.generators.grid_2d_graph(gsize,gsize) #grid graph gg
posg = nx.layout.fruchterman_reingold_layout(gg)
nx.draw(gg,posg)
center = posg[(0,0)]

ax = plt.gca()
c = plt.Circle(center, radius=0.1)
ax.add_patch(c)
plt.axis('equal')
plt.show()

[Daniel Schult]

I see two potential problems:

1) you need to add the circle to the axes.  See

http://stackoverflow.com/questions/9215658/plot-a-circle-with-pyplot

2) your radius is much larger than the position values of the nodes in the network. You could try radius=.15 (but you'll still need to add the circle to the axes).

Dan

[vjktmail]

Daniel, Aric,
thank you both!
I ran Aric's example successfully.  I didn't realize that I had to use the axes; I need to hit the pyplot documentation.
Thanks.