function [r,s] = spart2(A)

% SPART2 : supernode partition

%

% [r,x] = spart2(A) partitions the columns of A according to supernode 

% definition 2:

% A supernode in A = L+U is a sequence of adjacent columns in which

% the diagonal block of L is full,

% and below the diagonal all the columns (of L) have the same row structure.

% Output: row and column partitions r and s suitable for SPYPART(A,r,s)

%

% Copyright (c) 1995 by Xerox Corporation.  All rights reserved.

% HELP COPYRIGHT for complete copyright and licensing notice.

[nr,nc] = size(A);

A = spones(A);

A = tril(A) | speye(nr,nc);

A1 = tril([zeros(nr,1) A]);

A2 = [A ones(nr,1)];

signature = sum(xor(A1,A2));

r = find(signature);

r = r';

if nargout > 1,

    s = r;

    r = [1 nr+1];

end;