Graph Plotting

(For LaTeX drawings of graphs, see the graph_latex module.)

All graphs have an associated Sage graphics object, which you can display:

sage: G = graphs.WheelGraph(15)
sage: P = G.plot()
sage: P.show()  # long time

When plotting a graph created using Sage’s Graph command, node positions are determined using the spring-layout algorithm. Special graphs available from graphs.* have preset positions. For example, compare the two plots of the Petersen graph, as obtained using Graph or as obtained from that database:

sage: petersen_spring = Graph(':I`ES@obGkqegW~')
sage: petersen_spring.show()  # long time

sage: petersen_database = graphs.PetersenGraph()
sage: petersen_database.show()  # long time

All constructors in this database (except some random graphs) prefill the position dictionary, bypassing the spring-layout positioning algorithm.

Plot options

Here is the list of options accepted by plot() and the constructor of GraphPlot. Those two functions also accept all options of sage.plot.graphics.Graphics.show().

layout	A layout algorithm – one of : “acyclic”, “circular” (plots the graph with vertices evenly distributed on a circle), “ranked”, “graphviz”, “planar”, “spring” (traditional spring layout, using the graph’s current positions as initial positions), or “tree” (the tree will be plotted in levels, depending on minimum distance for the root).
iterations	The number of times to execute the spring layout algorithm.
heights	A dictionary mapping heights to the list of vertices at this height.
spring	Use spring layout to finalize the current layout.
tree_root	A vertex designation for drawing trees. A vertex of the tree to be used as the root for the layout='tree' option. If no root is specified, then one is chosen close to the center of the tree. Ignored unless layout='tree'.
forest_roots	An iterable specifying which vertices to use as roots for the layout='forest' option. If no root is specified for a tree, then one is chosen close to the center of the tree. Ignored unless layout='forest'.
tree_orientation	The direction of tree branches – ‘up’, ‘down’, ‘left’ or ‘right’.
save_pos	Whether or not to save the computed position for the graph.
dim	The dimension of the layout – 2 or 3.
prog	Which graphviz layout program to use – one of “circo”, “dot”, “fdp”, “neato”, or “twopi”.
by_component	Whether to do the spring layout by connected component – a boolean.
pos	The position dictionary of vertices.
vertex_labels	Whether or not to draw vertex labels.
vertex_color	Default color for vertices not listed in vertex_colors dictionary.
vertex_colors	A dictionary specifying vertex colors: each key is a color recognizable by matplotlib, and each corresponding value is a list of vertices.
vertex_size	The size to draw the vertices.
vertex_shape	The shape to draw the vertices. Currently unavailable for Multi-edged DiGraphs.
edge_labels	Whether or not to draw edge labels.
edge_style	The linestyle of the edges. It should be one of “solid”, “dashed”, “dotted”, dashdot”, or “-”, “–”, “:”, “-.”, respectively.
edge_thickness	The thickness of the edges.
edge_color	The default color for edges not listed in edge_colors.
edge_colors	A dictionary specifying edge colors: each key is a color recognized by matplotlib, and each corresponding value is a list of edges.
color_by_label	Whether to color the edges according to their labels. This also accepts a function or dictionary mapping labels to colors.
partition	A partition of the vertex set. If specified, plot will show each cell in a different color; vertex_colors takes precedence.
loop_size	The radius of the smallest loop.
dist	The distance between multiedges.
max_dist	The max distance range to allow multiedges.
talk	Whether to display the vertices in talk mode (larger and white).
graph_border	Whether or not to draw a frame around the graph.
edge_labels_background	The color of the background of the edge labels.

Default options

This module defines two dictionaries containing default options for the plot() and show() methods. These two dictionaries are sage.graphs.graph_plot.DEFAULT_PLOT_OPTIONS and sage.graphs.graph_plot.DEFAULT_SHOW_OPTIONS, respectively.

Obviously, these values are overruled when arguments are given explicitly.

Here is how to define the default size of a graph drawing to be (6, 6). The first two calls to show() use this option, while the third does not (a value for figsize is explicitly given):

sage: import sage.graphs.graph_plot
sage: sage.graphs.graph_plot.DEFAULT_SHOW_OPTIONS['figsize'] = (6, 6)
sage: graphs.PetersenGraph().show()  # long time
sage: graphs.ChvatalGraph().show()  # long time
sage: graphs.PetersenGraph().show(figsize=(4, 4))  # long time

We can now reset the default to its initial value, and now display graphs as previously:

sage: sage.graphs.graph_plot.DEFAULT_SHOW_OPTIONS['figsize'] = (4, 4)
sage: graphs.PetersenGraph().show()  # long time
sage: graphs.ChvatalGraph().show()  # long time

Note

• While DEFAULT_PLOT_OPTIONS affects both G.show() and G.plot(), settings from DEFAULT_SHOW_OPTIONS only affects G.show().

• In order to define a default value permanently, you can add a couple of lines to Sage’s startup scripts. Example:

  sage: import sage.graphs.graph_plot
  sage: sage.graphs.graph_plot.DEFAULT_SHOW_OPTIONS['figsize'] = (4, 4)
  

Index of methods and functions

GraphPlot.set_pos()	Set the position plotting parameters for this GraphPlot.
GraphPlot.set_vertices()	Set the vertex plotting parameters for this GraphPlot.
GraphPlot.set_edges()	Set the edge (or arrow) plotting parameters for the GraphPlot object.
GraphPlot.show()	Show the (Di)Graph associated with this GraphPlot object.
GraphPlot.plot()	Return a graphics object representing the (di)graph.
GraphPlot.layout_tree()	Compute a nice layout of a tree.

class sage.graphs.graph_plot.GraphPlot(graph, options)

Bases: sage.structure.sage_object.SageObject

Return a GraphPlot object, which stores all the parameters needed for plotting (Di)Graphs.

A GraphPlot has a plot and show function, as well as some functions to set parameters for vertices and edges. This constructor assumes default options are set. Defaults are shown in the example below.

EXAMPLES:

sage: from sage.graphs.graph_plot import GraphPlot
sage: options = {
....:     'vertex_size': 200,
....:     'vertex_labels': True,
....:     'layout': None,
....:     'edge_style': 'solid',
....:     'edge_color': 'black',
....:     'edge_colors': None,
....:     'edge_labels': False,
....:     'iterations': 50,
....:     'tree_orientation': 'down',
....:     'heights': None,
....:     'graph_border': False,
....:     'talk': False,
....:     'color_by_label': False,
....:     'partition': None,
....:     'dist': .075,
....:     'max_dist': 1.5,
....:     'loop_size': .075,
....:     'edge_labels_background': 'transparent'}
sage: g = Graph({0: [1, 2], 2: [3], 4: [0, 1]})
sage: GP = GraphPlot(g, options)

layout_tree(root, orientation)

Compute a nice layout of a tree.

INPUT:

• root – the root vertex.

• orientation – whether to place the root at the top or at the bottom:

  • orientation="down" – children are placed below their parent

  • orientation="top" – children are placed above their parent

EXAMPLES:

sage: from sage.graphs.graph_plot import GraphPlot
sage: G = graphs.HoffmanSingletonGraph()
sage: T = Graph()
sage: T.add_edges(G.min_spanning_tree(starting_vertex=0))
sage: T.show(layout='tree', tree_root=0)  # indirect doctest

plot(**kwds)

Return a graphics object representing the (di)graph.

INPUT:

The options accepted by this method are to be found in the documentation of the sage.graphs.graph_plot module, and the show() method.

Note

See the module's documentation for information on default values of this method.

We can specify some pretty precise plotting of familiar graphs:

sage: from math import sin, cos, pi
sage: P = graphs.PetersenGraph()
sage: d = {'#FF0000': [0, 5], '#FF9900': [1, 6], '#FFFF00': [2, 7],
....:      '#00FF00': [3, 8], '#0000FF': [4,9]}
sage: pos_dict = {}
sage: for i in range(5):
....:  x = float(cos(pi/2 + ((2*pi)/5)*i))
....:  y = float(sin(pi/2 + ((2*pi)/5)*i))
....:  pos_dict[i] = [x,y]
...
sage: for i in range(5, 10):
....:  x = float(0.5*cos(pi/2 + ((2*pi)/5)*i))
....:  y = float(0.5*sin(pi/2 + ((2*pi)/5)*i))
....:  pos_dict[i] = [x,y]
...
sage: pl = P.graphplot(pos=pos_dict, vertex_colors=d)
sage: pl.show()

Here are some more common graphs with typical options:

sage: C = graphs.CubeGraph(8)
sage: P = C.graphplot(vertex_labels=False, vertex_size=0,
....:                 graph_border=True)
sage: P.show()

sage: G = graphs.HeawoodGraph().copy(sparse=True)
sage: for u, v, l in G.edges():
....:     G.set_edge_label(u, v, f'({u},{v})')
sage: G.graphplot(edge_labels=True).show()

The options for plotting also work with directed graphs:

sage: D = DiGraph({
....:     0: [1, 10, 19], 1: [8, 2], 2: [3, 6], 3: [19, 4],
....:     4: [17, 5], 5: [6, 15], 6: [7], 7: [8, 14], 8: [9],
....:     9: [10, 13], 10: [11], 11: [12, 18], 12: [16, 13],
....:     13: [14], 14: [15], 15: [16], 16: [17], 17: [18],
....:     18: [19], 19: []})
sage: for u, v, l in D.edges():
....:     D.set_edge_label(u, v, f'({u},{v})')
sage: D.graphplot(edge_labels=True, layout='circular').show()

This example shows off the coloring of edges:

sage: from sage.plot.colors import rainbow
sage: C = graphs.CubeGraph(5)
sage: R = rainbow(5)
sage: edge_colors = {}
sage: for i in range(5):
....:     edge_colors[R[i]] = []
sage: for u, v, l in C.edges():
....:     for i in range(5):
....:         if u[i] != v[i]:
....:             edge_colors[R[i]].append((u, v, l))
sage: C.graphplot(vertex_labels=False, vertex_size=0,
....:             edge_colors=edge_colors).show()

With the partition option, we can separate out same-color groups of vertices:

sage: D = graphs.DodecahedralGraph()
sage: Pi = [[6, 5, 15, 14, 7], [16, 13, 8, 2, 4],
....:       [12, 17, 9, 3, 1], [0, 19, 18, 10, 11]]
sage: D.show(partition=Pi)

Loops are also plotted correctly:

sage: G = graphs.PetersenGraph()
sage: G.allow_loops(True)
sage: G.add_edge(0,0)
sage: G.show()

sage: D = DiGraph({0:[0,1], 1:[2], 2:[3]}, loops=True)
sage: D.show()
sage: D.show(edge_colors={(0, 1, 0): [(0, 1, None), (1, 2, None)],
....:                     (0, 0, 0): [(2, 3, None)]})

More options:

sage: pos = {0: [0.0, 1.5], 1: [-0.8, 0.3], 2: [-0.6, -0.8],
....:        3:[0.6, -0.8], 4:[0.8, 0.3]}
sage: g = Graph({0: [1], 1: [2], 2: [3], 3: [4], 4: [0]})
sage: g.graphplot(pos=pos, layout='spring', iterations=0).plot()
Graphics object consisting of 11 graphics primitives

sage: G = Graph()
sage: P = G.graphplot().plot()
sage: P.axes()
False
sage: G = DiGraph()
sage: P = G.graphplot().plot()
sage: P.axes()
False

We can plot multiple graphs:

sage: T = list(graphs.trees(7))
sage: t = T[3]
sage: t.graphplot(heights={0: [0], 1: [4, 5, 1],
....:                      2: [2], 3: [3, 6]}
....:            ).plot()
Graphics object consisting of 14 graphics primitives

sage: T = list(graphs.trees(7))
sage: t = T[3]
sage: t.graphplot(heights={0: [0], 1: [4, 5, 1],
....:                      2: [2], 3: [3, 6]}
....:            ).plot()
Graphics object consisting of 14 graphics primitives

sage: t.set_edge_label(0, 1, -7)
sage: t.set_edge_label(0, 5, 3)
sage: t.set_edge_label(0, 5, 99)
sage: t.set_edge_label(1, 2, 1000)
sage: t.set_edge_label(3, 2, 'spam')
sage: t.set_edge_label(2, 6, 3/2)
sage: t.set_edge_label(0, 4, 66)
sage: t.graphplot(heights={0: [0], 1: [4, 5, 1],
....:                      2: [2], 3: [3, 6]},
....:             edge_labels=True
....:            ).plot()
Graphics object consisting of 20 graphics primitives

sage: T = list(graphs.trees(7))
sage: t = T[3]
sage: t.graphplot(layout='tree').show()

The tree layout is also useful:

sage: t = DiGraph('JCC???@A??GO??CO??GO??')
sage: t.graphplot(layout='tree', tree_root=0,
....:             tree_orientation="up"
....:            ).show()

More examples:

sage: D = DiGraph({0:[1,2,3], 2:[1,4], 3:[0]})
sage: D.graphplot().show()

sage: D = DiGraph(multiedges=True, sparse=True)
sage: for i in range(5):
....:   D.add_edge((i, i + 1, 'a'))
....:   D.add_edge((i, i - 1, 'b'))
sage: D.graphplot(edge_labels=True,
....:             edge_colors=D._color_by_label()
....:            ).plot()
Graphics object consisting of 34 graphics primitives

sage: g = Graph({}, loops=True, multiedges=True, sparse=True)
sage: g.add_edges([(0, 0, 'a'), (0, 0, 'b'), (0, 1, 'c'),
....:              (0, 1, 'd'), (0, 1, 'e'), (0, 1, 'f'),
....:              (0, 1, 'f'), (2, 1, 'g'), (2, 2, 'h')])
sage: g.graphplot(edge_labels=True,
....:             color_by_label=True,
....:             edge_style='dashed'
....:            ).plot()
Graphics object consisting of 22 graphics primitives

The edge_style option may be provided in the short format too:

sage: g.graphplot(edge_labels=True,
....:             color_by_label=True,
....:             edge_style='--'
....:            ).plot()
Graphics object consisting of 22 graphics primitives

set_edges(**edge_options)

Set edge plotting parameters for the GraphPlot object.

This function is called by the constructor but can also be called to update the vertex options of an existing GraphPlot object. Note that the changes are cumulative.

EXAMPLES:

sage: g = Graph(loops=True, multiedges=True, sparse=True)
sage: g.add_edges([(0, 0, 'a'), (0, 0, 'b'), (0, 1, 'c'),
....:              (0, 1, 'd'), (0, 1, 'e'), (0, 1, 'f'),
....:              (0, 1, 'f'), (2, 1, 'g'), (2, 2, 'h')])
sage: GP = g.graphplot(vertex_size=100, edge_labels=True,
....:                  color_by_label=True, edge_style='dashed')
sage: GP.set_edges(edge_style='solid')
sage: GP.plot()
Graphics object consisting of 22 graphics primitives

sage: GP.set_edges(edge_color='black')
sage: GP.plot()
Graphics object consisting of 22 graphics primitives

sage: d = DiGraph(loops=True, multiedges=True, sparse=True)
sage: d.add_edges([(0, 0, 'a'), (0, 0, 'b'), (0, 1, 'c'),
....:              (0, 1, 'd'), (0, 1, 'e'), (0, 1, 'f'),
....:              (0, 1, 'f'), (2, 1, 'g'), (2, 2, 'h')])
sage: GP = d.graphplot(vertex_size=100, edge_labels=True,
....:                  color_by_label=True, edge_style='dashed')
sage: GP.set_edges(edge_style='solid')
sage: GP.plot()
Graphics object consisting of 24 graphics primitives

sage: GP.set_edges(edge_color='black')
sage: GP.plot()
Graphics object consisting of 24 graphics primitives

set_pos()

Set the position plotting parameters for this GraphPlot.

EXAMPLES:

This function is called implicitly by the code below:

sage: g = Graph({0: [1, 2], 2: [3], 4: [0, 1]})
sage: g.graphplot(save_pos=True, layout='circular')  # indirect doctest
GraphPlot object for Graph on 5 vertices

The following illustrates the format of a position dictionary, but due to numerical noise we do not check the values themselves:

sage: g.get_pos()
{0: (0.0, 1.0),
 1: (-0.951..., 0.309...),
 2: (-0.587..., -0.809...),
 3: (0.587..., -0.809...),
 4: (0.951..., 0.309...)}

sage: T = list(graphs.trees(7))
sage: t = T[3]
sage: t.plot(heights={0: [0], 1: [4, 5, 1], 2: [2], 3: [3, 6]})
Graphics object consisting of 14 graphics primitives

set_vertices(**vertex_options)

Set the vertex plotting parameters for this GraphPlot.

This function is called by the constructor but can also be called to make updates to the vertex options of an existing GraphPlot object. Note that the changes are cumulative.

EXAMPLES:

sage: g = Graph({}, loops=True, multiedges=True, sparse=True)
sage: g.add_edges([(0, 0, 'a'), (0, 0, 'b'), (0, 1, 'c'),
....:              (0, 1, 'd'), (0, 1, 'e'), (0, 1, 'f'),
....:              (0, 1, 'f'), (2, 1, 'g'), (2, 2, 'h')])
sage: GP = g.graphplot(vertex_size=100, edge_labels=True,
....:                  color_by_label=True, edge_style='dashed')
sage: GP.set_vertices(talk=True)
sage: GP.plot()
Graphics object consisting of 22 graphics primitives
sage: GP.set_vertices(vertex_color='green', vertex_shape='^')
sage: GP.plot()
Graphics object consisting of 22 graphics primitives

show(**kwds)

Show the (di)graph associated with this GraphPlot object.

INPUT:

This method accepts all parameters of sage.plot.graphics.Graphics.show().

Note

• See the module's documentation for information on default values of this method.

• Any options not used by plot will be passed on to the show() method.

EXAMPLES:

sage: C = graphs.CubeGraph(8)
sage: P = C.graphplot(vertex_labels=False, vertex_size=0,
....:                 graph_border=True)
sage: P.show()