NAME

Graph::Writer::Graph6 - write Graph.pm in graph6, sparse6 or digraph6 format

SYNOPSIS

 use Graph::Writer::Graph6;
 my $writer = Graph::Writer::Graph6->new;
 $writer->write_graph($graph, 'filename.txt');
 $writer->write_graph($graph, $filehandle);

 # or one-off create and use
 Graph::Writer::Graph6->new->write_graph($graph,'filename.txt');

CLASS HIERARCHY

Graph::Writer::Graph6 is a subclass of Graph::Writer.

    Graph::Writer
      Graph::Writer::Graph6

DESCRIPTION

Graph::Writer::Graph6 writes a Graph.pm graph to a file or file handle in graph6, sparse6 or digraph6 format. These formats are per

http://cs.anu.edu.au/~bdm/data/formats.txt

graph6 represents an undirected graph with no self-loops or multi-edges. Any self-loops in $graph are ignored. Multi-edges are written just once, and if $graph is directed then an edge of either direction is written.

sparse6 represents an undirected graph possibly with multi-edges and self-loops. If $graph is directed then an edge in either direction is written. If there's edges both ways then a multi-edge is written.

digraph6 represents a directed graph, possibly with self-loops but no multi-edges. Any multi-edges in $graph are written just once. If $graph is undirected then an edge in written in both directions (though usually graph6 or sparse6 would be preferred for undirected).

The formats have no vertex names and no attributes. In the current implementation $graph->vertices() is sorted alphabetically (sort) to give a consistent (though slightly arbitrary) vertex numbering.

See Graph::Graph6 for further notes on the formats. See examples/graph-random.pl for a complete sample program.

FUNCTIONS

$writer = Graph::Writer::Graph6->new (key => value, ...)

Create and return a new writer object. The key/value options are

    format   => "graph6", "sparse6" or "digraph6",
                  string, default "graph6"
    header   => boolean, default false

If header is true then write a header >>graph6<<, >>sparse6<< or >>digraph6<< as appropriate.

$writer->write_graph($graph, $filename_or_fh)

Write $graph to $filename_or_fh in the selected format.

$graph is either a Graph.pm object or something sufficiently compatible. There's no check on the actual class of $graph. (Don't mistakenly pass a Graph::Easy here. It's close enough that it runs, but doesn't give a consistent vertex order and might miss edges on undirected graphs.)

$filename_or_fh can be a string filename. The file is replaced with the graph.

$filename_or_fh can be a reference which is taken to be a file handle and the graph is written to it. Multiple graphs can be written to a handle one after the other to make a file or other output of several graphs. The format includes a final newline "\n" terminator in all cases.

    my $writer = Graph::Writer::Graph6->new;
    $writer->write_graph($graph1, \*STDOUT);
    $writer->write_graph($graph2, \*STDOUT);

BUGS

Writing a big graph in graph6 and digraph6 format is not particularly fast. The current implementation uses Graph.pm method has_edge() and makes O(N^2) calls to it for a graph of N vertices. The overhead of this becomes significant for big graphs. For a graph of relatively few edges getting all edges() at once would be faster, but in that case writing sparse6 would be both smaller and faster, if that format is suitable for a given application.

Graph.pm 0.96 had a bug on multiedged undirected graphs where its edges() method sometimes did not return all the edges of the graph, causing sparse6 output to miss some edges. This likely affects other things too so use version 0.97 for such a graph (or countedged undirected was ok if that suits).

SEE ALSO

Graph, Graph::Writer, Graph::Writer::Sparse6

Graph::Graph6, nauty-showg(1), nauty-copyg(1)

HOME PAGE

http://user42.tuxfamily.org/graph-graph6/index.html

LICENSE

Copyright 2015, 2016, 2017, 2018 Kevin Ryde

Graph-Graph6 is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.

Graph-Graph6 is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with Graph-Graph6. If not, see http://www.gnu.org/licenses/.