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function Graph = graph (G, varargin)
%GRAPH convert a GraphBLAS matrix into a undirected Graph.
% Graph = graph (G) converts a GraphBLAS matrix G into an undirected
% Graph. G is assumed to be symmetric; only tril (G) is used by default.
% G must be square. If G is logical, then no weights are added to the
% Graph. If G is single or double, these become the weights of the
% Graph. If G is integer, the Graph is constructed with weights of type
% double.
%
% Graph = graph (G, ..., 'upper') uses triu (G) to construct the Graph.
% Graph = graph (G, ..., 'lower') uses tril (G) to construct the Graph.
% The default is 'lower'.
%
% Graph = graph (G, ..., 'omitselfloops') ignores the diagonal of G, and
% the resulting Graph has no self-edges. The default is that
% self-edges are created from any diagonal entries of G.
%
% Example:
%
% G = GrB (bucky) ;
% Graph = graph (G)
% plot (Graph)
%
% See also graph, digraph, GrB/digraph.
% SuiteSparse:GraphBLAS, Timothy A. Davis, (c) 2017-2022, All Rights Reserved.
% SPDX-License-Identifier: Apache-2.0
G = G.opaque ;
[m, n, type] = gbsize (G) ;
if (m ~= n)
error ('GrB:error', 'G must be square') ;
end
% get the string options
side = 'lower' ;
omitself = false ;
for k = 1:nargin-1
arg = lower (varargin {k}) ;
switch arg
case { 'upper', 'lower' }
side = arg ;
case { 'omitselfloops' }
omitself = true ;
otherwise
error ('GrB:error', 'unknown option') ;
end
end
% apply the options
if (omitself)
% ignore diagonal entries of G
if (isequal (side, 'upper'))
G = gbselect ('triu', G, 1) ;
elseif (isequal (side, 'lower'))
G = gbselect ('tril', G, -1) ;
end
else
% include diagonal entries of G
if (isequal (side, 'upper'))
G = gbselect ('triu', G, 0) ;
elseif (isequal (side, 'lower'))
G = gbselect ('tril', G, 0) ;
end
end
% construct the graph
switch (type)
case { 'single' }
% The graph(...) function can accept x as single, but not
% from a built-in sparse matrix. So extract the tuples of G first.
[i, j, x] = gbextracttuples (G) ;
Graph = graph (i, j, x, n) ;
case { 'logical' }
% The digraph(...) function allows for logical
% adjacency matrices (no edge weights are created).
Graph = graph (gbbuiltin (G, 'logical'), side) ;
otherwise
% typecast to double
Graph = graph (gbbuiltin (G, 'double'), side) ;
end
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