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function [p, q, r, s] = ccspy (A, bipartite, res)
%CCSPY plot the connected components of a matrix.
%
% Example:
% [p, q, r, s] = ccspy (A, bipartite, res)
%
% If A is square, [p,q,r,s] = ccspy(A) finds a permutation p so that A(p,q)
% is permuted into block upper triangular form. In this case, r=s, p=q and
% the kth diagonal block is given by A (t,t) where t = r(k):r(k+1)-1.
% The diagonal of A is ignored.
%
% If A is not square (or for [p,q,r,s] = ccspy(A,1)), then the connected
% components of the bipartite graph of A are found. A(p,q) is permuted into
% block diagonal form, where the diagonal blocks are rectangular. The kth
% block is given by A(r(k):r(k+1)-1,s(k):s(k+1)-1). A can be rectangular.
%
% It then plots the result via cspy, drawing a greenbox around each component.
% A 3rd input argument (res) controls the resolution (see cspy for a
% description of the res parameter).
%
% See also CSPY, CS_DMPERM, DMPERM, CS_SCC, CS_SCC2, CS_DMSPY.
% CXSparse, Copyright (c) 2006-2022, Timothy A. Davis. All Rights Reserved.
% SPDX-License-Identifier: LGPL-2.1+
if (~issparse (A))
A = sparse (A) ;
end
[m n] = size (A) ;
if (nargin < 3)
res = 256 ;
end
if (nargin < 2)
bipartite = [ ] ;
end
if (isempty (bipartite))
bipartite = (m ~= n) ;
end
% find the strongly connected components
[p1 q r s] = cs_scc2 (A, bipartite) ;
if (nargout > 0)
p = p1 ;
end
nb = length (r)-1 ;
% plot the result
S = A (p1,q) ;
if (res == 0)
spy (S) ;
e = 1 ;
else
e = cspy (S,res) ;
end
hold on
title (sprintf ('%d-by-%d, strongly connected commponents: %d\n', m, n, nb)) ;
if (~bipartite)
plot ([.5 .5 n+.5 n+.5], [.5 .5 n+.5 n+.5], 'r') ;
end
drawboxes (nb, e, r, s) ;
drawbox (1,m+1,1,n+1,'k',1,e) ;
hold off
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