# kwant.graph.CGraph¶

class kwant.graph.CGraph[source]

Bases: object

A compressed graph which can be efficiently queried for the existence of edges and outgoing neighbors.

Objects of this class do not initialize the members themselves, but expect that they hold usable values. A good way to create them is by compressing a Graph.

Iterating over a graph yields a sequence of (tail, head) pairs of all edges. The number of an edge in this sequence equals its edge ID. The built-in function enumerate can thus be used to easily iterate over all edges along with their edge IDs.

Methods

all_edge_ids()[source]

Return an iterator over all edge IDs of edges with a given tail and head.

Parameters: tail : integer head : integer edge_id : integer NodeDoesNotExist EdgeDoesNotExistError DisabledFeatureError If tail is negative and the graph is not two-way compressed.
edge_id()[source]

Return the edge ID of an edge given its sequential number.

Parameters: edge_nr : integer edge_id : integer DisabledFeatureError If edge_nr_translation was not enabled during graph compression. EdgeDoesNotExistError
first_edge_id()[source]

Return the edge ID of the first edge (tail, head).

Parameters: tail : integer head : integer edge_id : integer NodeDoesNotExist EdgeDoesNotExistError DisabledFeatureError If tail is negative and the graph is not two-way compressed.

Notes

This method is useful for graphs where each edge occurs only once.

has_dangling_edges()[source]
has_edge()[source]

Does the graph contain the edge (tail, head)?

Parameters: tail : integer head : integer had_edge : boolean NodeDoesNotExistError EdgeDoesNotExistError DisabledFeatureError If tail is negative and the graph is not two-way compressed.
head()[source]

Return the head of an edge, given its edge ID.

Parameters: edge_id : integer EdgeDoesNotExistError

Notes

This method executes in constant time. It works for all edge IDs, returning both positive and negative heads.

in_edge_ids()[source]

Return the IDs of incoming edges of a node.

Parameters: node : integer edge_ids : sequence of integers NodeDoesNotExistError DisabledFeatureError If the graph is not two-way compressed.
in_neighbors()[source]

Return the nodes which point to a node.

Parameters: node : integer nodes : sequence of integers NodeDoesNotExistError DisabledFeatureError If the graph is not two-way compressed.
out_edge_ids()[source]

Return the IDs of outgoing edges of node.

Parameters: node : integer edge_ids : sequence of integers NodeDoesNotExistError
out_neighbors()[source]

Return the nodes a node points to.

Parameters: node : integer nodes : sequence of integers NodeDoesNotExistError
tail()[source]

Return the tail of an edge, given its edge ID.

Parameters: edge_id : integer tail : integer If the edge exists and is positive. None If the tail is negative. EdgeDoesNotExistError

Notes

The average performance of this method is O(log num_nodes) for non-negative tails and O(1) for negative ones.

write_dot()[source]

Write a representation of the graph in dot format to file.

Parameters: file : file-like object

Notes

That resulting file can be visualized with dot(1) or neato(1) form the graphviz package.

Attributes

edge_nr_translation[source]
num_edges[source]
num_nodes[source]
num_px_edges[source]
num_xp_edges[source]
twoway[source]

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