28 lines
752 B
Matlab
28 lines
752 B
Matlab
function [r,s] = spart2(A)
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% SPART2 : supernode partition
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%
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% [r,x] = spart2(A) partitions the columns of A according to supernode
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% definition 2:
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% A supernode in A = L+U is a sequence of adjacent columns in which
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% the diagonal block of L is full,
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% and below the diagonal all the columns (of L) have the same row structure.
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% Output: row and column partitions r and s suitable for SPYPART(A,r,s)
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%
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% Copyright (c) 1995 by Xerox Corporation. All rights reserved.
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% HELP COPYRIGHT for complete copyright and licensing notice.
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[nr,nc] = size(A);
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A = spones(A);
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A = tril(A) | speye(nr,nc);
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A1 = tril([zeros(nr,1) A]);
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A2 = [A ones(nr,1)];
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signature = sum(xor(A1,A2));
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r = find(signature);
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r = r';
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if nargout > 1,
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s = r;
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r = [1 nr+1];
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end;
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