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function [G_coarse, A_coarse, map] = safe_coarsen(G, O, A)
%SAFE_COARSEN coarsen a graph after attempting to sanitize it.
% safe_coarsen(G) computes a matching of vertices in the graph G
% and then coarsens the graph by combining all matched vertices into
% supervertices. With no option struct specified, the coarsening is done
% using a combination of heavy-edge matching and other more aggressive
% techniques to avoid stalling. An optional vertex weight vector A can
% also be specified, and a fine-to-coarse mapping of vertices can also
% be obtained (e.g. map(vertex_fine) = vertex_coarse).
%
% [G_coarse, A_coarse, map] = safe_coarsen(G) sanitizes and then coarsens a
% graph represented with sparse adjacency matrix G. G_coarse is the coarsened
% adjacency matrix, A_coarse is the coarsened array of vertex weights, and
% map is a mapping of original vertices to coarsened vertices.
%
% [G_coarse, A_coarse, map] = safe_coarsen(G, O) uses the option struct O to
% specify coarsening options (e.g. matching strategies).
%
% [G_coarse, A_coarse, map] = safe_coarsen(G, O, A) uses the array A as
% vertex weights, such that A(i) is the vertex weight of vertex i. If A is
% not specified, A is assumed to be an array of all ones (all weights are 1).
%
% Example:
% Prob = ssget('DNVS/troll'); G = Prob.A;
% G_coarse = safe_coarsen(G);
% spy(G_coarse);
%
% See also COARSEN, EDGECUT_OPTIONS.
% Copyright (c) 2018, N. Yeralan, S. Kolodziej, T. Davis, W. Hager
% SPDX-License-Identifier: GPL-3.0-only
G_safe = sanitize(G);
if (nargin == 1)
[G_coarse, A_coarse, map] = coarsen(G_safe);
elseif (nargin == 2)
[G_coarse, A_coarse, map] = coarsen(G_safe, O);
else
[G_coarse, A_coarse, map] = coarsen(G_safe, O, A);
end
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