python-igraph API reference

List of all classes, functions and methods in python-igraph

igraph.VertexCover

class documentation

class VertexCover(Cover):

Known subclasses: igraph.CohesiveBlocks

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The cover of the vertex set of a graph.

This class extends Cover by linking it to a specific Graph object. It also provides some handy methods like getting the subgraph corresponding to a cluster and such.

Note
since this class is linked to a Graph, destroying the graph by the del operator does not free the memory occupied by the graph if there exists a VertexCover that references the Graph.
Method __init__ Creates a cover object for a given graph.
Method __plot__ Plots the cover to the given Cairo context or matplotlib Axes.
Method crossing Returns a boolean vector where element i is True iff edge i lies between clusters, False otherwise.
Method subgraph Get the subgraph belonging to a given cluster.
Method subgraphs Gets all the subgraphs belonging to each of the clusters.
Property graph Returns the graph belonging to this object
Method _formatted_cluster_iterator Iterates over the clusters and formats them into a string to be presented in the summary.
Instance Variable _graph Undocumented

Inherited from Cover:

Method __getitem__ Returns the cluster with the given index.
Method __iter__ Iterates over the clusters in this cover.
Method __len__ Returns the number of clusters in this cover.
Method __str__ Returns a string representation of the cover.
Method size Returns the size of a given cluster.
Method size_histogram Returns the histogram of cluster sizes.
Method sizes Returns the size of given clusters.
Method summary Returns the summary of the cover.
Property membership Returns the membership vector of this cover.
Property n Returns the number of elements in the set covered by this cover.
Instance Variable _clusters Undocumented
Instance Variable _n Undocumented
def __init__(self, graph, clusters=None):
overrides igraph.Cover.__init__
overridden in igraph.CohesiveBlocks

Creates a cover object for a given graph.

Parameters
graphthe graph that will be associated to the cover
clustersthe list of clusters. If None, it is assumed that there is only a single cluster that covers the whole graph.
def __plot__(self, backend, context, *args, **kwds):
overridden in igraph.CohesiveBlocks

Plots the cover to the given Cairo context or matplotlib Axes.

This is done by calling Graph.__plot__() with the same arguments, but drawing nice colored blobs around the vertex groups.

This method understands all the positional and keyword arguments that are understood by Graph.__plot__(), only the differences will be highlighted here:

  • mark_groups: whether to highlight the vertex clusters by colored polygons. Besides the values accepted by Graph.__plot__ (i.e., a dict mapping colors to vertex indices, a list containing lists of vertex indices, or False), the following are also accepted:

    • True: all the clusters will be highlighted, the colors matching the corresponding color indices from the current palette (see the palette keyword argument of Graph.__plot__.
    • A dict mapping cluster indices or tuples of vertex indices to color names. The given clusters or vertex groups will be highlighted by the given colors.
    • A list of cluster indices. This is equivalent to passing a dict mapping numeric color indices from the current palette to cluster indices; therefore, the cluster referred to by element i of the list will be highlighted by color i from the palette.

    The value of the plotting.mark_groups configuration key is also taken into account here; if that configuration key is True and mark_groups is not given explicitly, it will automatically be set to True.

    In place of lists of vertex indices, you may also use VertexSeq instances.

    In place of color names, you may also use color indices into the current palette. None as a color name will mean that the corresponding group is ignored.

  • palette: the palette used to resolve numeric color indices to RGBA values. By default, this is an instance of ClusterColoringPalette.

See Also
Graph.__plot__() for more supported keyword arguments.
def crossing(self):

Returns a boolean vector where element i is True iff edge i lies between clusters, False otherwise.

def subgraph(self, idx):

Get the subgraph belonging to a given cluster.

Precondition: the vertex set of the graph hasn't been modified since the moment the cover was constructed.

Parameters
idxthe cluster index
Returns
a copy of the subgraph
def subgraphs(self):

Gets all the subgraphs belonging to each of the clusters.

Precondition: the vertex set of the graph hasn't been modified since the moment the cover was constructed.

Returns
a list containing copies of the subgraphs
@property
graph =

Returns the graph belonging to this object

def _formatted_cluster_iterator(self):
overrides igraph.Cover._formatted_cluster_iterator

Iterates over the clusters and formats them into a string to be presented in the summary.

_graph =

Undocumented