ASKSAGE: Sage Q&A Forum - RSS feedhttps://ask.sagemath.org/questions/Q&A Forum for SageenCopyright Sage, 2010. Some rights reserved under creative commons license.Tue, 27 Sep 2022 20:55:16 +0200Code for deleting the edges of a subgraphhttps://ask.sagemath.org/question/64205/code-for-deleting-the-edges-of-a-subgraph/Hi all,
I have as inputs a simple graph G and a subgraph H. I want as output the graph G-H, defined as the graph obtained from G by removing the edges of H (without removing any vertices).
H is given like this:
H=G.random_subgraph(.25)
Is there a command like G.delete_edges(H) that returns the desired graph?
Thank you.MagusTue, 27 Sep 2022 20:55:16 +0200https://ask.sagemath.org/question/64205/Edge color for undirected multiedge graphshttps://ask.sagemath.org/question/39153/edge-color-for-undirected-multiedge-graphs/ It seems that there is a bug with specifying the color of undirected multiedges. Here's an example:
G=graphs.PathGraph(2)
G.allow_multiple_edges(True)
G.add_edge((0,1))
G.plot(edge_colors={"red":[(1,0)]})
The graph plotted has then four edges, two black and two red. It seems that the multiedge to be colored red is seen as a different one than the already present one, even though they are actually the same since the graph is undirected. I get the intended plot if I change the last line to:
G.plot(edge_colors={"red":[(0,1)]})AckslFri, 13 Oct 2017 16:00:23 +0200https://ask.sagemath.org/question/39153/edge_style for different edges in a multigraphhttps://ask.sagemath.org/question/33228/edge_style-for-different-edges-in-a-multigraph/I'm trying to make a directed multigraph in which different edges have colors/edge styles so that they can be easy read either in color or in black and white.
I can make a graph with different colors:
D = DiGraph(multiedges=True)
var('A,B')
D.add_edge(A,B,'edge1')
D.add_edge(A,B,'edge2')
D.graphplot(color_by_label={'edge1':'green','edge2':'blue'}).show()
I can also make a graph with different styles, but overlayed:
G1 = DiGraph(multiedges=True)
G2 = DiGraph(multiedges=True)
var('A,B')
G1.add_edge(A,B,'edge1')
G2.add_edge(A,B,'edge2')
G1.set_pos({A:[0,0],B:[1,0]})
G2.set_pos({A:[0,0],B:[1,0]})
G = G1.graphplot(color_by_label={'edge1':'green'}, edge_style='--').plot() + G2.graphplot(color_by_label={'edge2':'blue'}, edge_style=':').plot()
G.show(axes=False)
and a very hack-y solution which looks nicer, but still bad:
G1 = DiGraph(multiedges=True)
G2 = DiGraph(multiedges=True)
var('A,B')
G1.add_edge(A,B,'edge1')
G2.add_edge(A,B,'edge2')
G1.add_edge(A,B,'edge2')
G2.add_edge(A,B,'edge1')
G1.set_pos({A:[0,0],B:[1,0]})
G2.set_pos({A:[0,0],B:[1,0]})
G = G1.graphplot(color_by_label={'edge1':'green','edge2':'white'}, edge_style='--').plot() + G2.graphplot(color_by_label={'edge2':'blue','edge1':'white'}, edge_style=':').plot()
G.show(axes=False)
I'd love to be able to have a multigraph where the edges are both different colors and different styles and don't completely overlap, but I'm not seeing a way to do this. Any help is appreciated!mthomasTue, 26 Apr 2016 02:17:33 +0200https://ask.sagemath.org/question/33228/enumerate subgraphs with edge setshttps://ask.sagemath.org/question/10969/enumerate-subgraphs-with-edge-sets/Hi,
I have been using Sage for the past few months now, and I use the subgraph_search_iterator() heavily. So far, I did not care for the edge set of the subgraph found. But now that I do, it seems that the subgraph_search_iterator() returns only the vertex sets of the corresponding subgraphs.
In particular, I am looking for subdivisions of K3,3 in an input graph. But I want the additional constraint that two fixed vertices (say, u and v) must be branch vertices of the subgraph found - by branch vertices I mean vertices of degree exactly 3 in the subgraph.
Any help would be greatly appreciated.
Thanks!nkothariTue, 28 Jan 2014 00:32:09 +0100https://ask.sagemath.org/question/10969/