63 lines
1.7 KiB
Mathematica
63 lines
1.7 KiB
Mathematica
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function x = lusolve(A,b,Pcol)
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% LUSOLVE : Solve linear systems by supernodal LU factorization.
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%
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% x = lusolve(A, b) returns the solution to the linear system A*x = b,
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% using a supernodal LU factorization that is faster than Matlab's
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% builtin LU. This m-file just calls a mex routine to do the work.
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%
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% By default, A is preordered by column minimum degree before factorization.
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% Optionally, the user can supply a desired column ordering:
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%
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% x = lusolve(A, b, pcol) uses pcol as a column permutation.
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% It still returns x = A\b, but it factors A(:,pcol) (if pcol is a
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% permutation vector) or A*Pcol (if Pcol is a permutation matrix).
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%
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% x = lusolve(A, b, 0) suppresses the default minimum degree ordering;
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% that is, it forces the identity permutation on columns.
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%
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% See also SUPERLU.
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%
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% John Gilbert, 6 April 1995
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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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[m,n] = size(A);
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if m ~= n
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error('matrix must be square');
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end;
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[mb,nb] = size(b);
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if mb ~= n
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error('right-hand side must have same row dimension as matrix');
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end;
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if n == 0
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x = [];
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return;
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end;
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% As necessary, compute the column permutation, and
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% convert it from a permutation vector to a permutation matrix
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% to fit the internal data structures of mexlusolve.
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if nargin < 3
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Pcol = colamd(A);
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end;
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if isempty(Pcol) | Pcol == 0
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Pcol = speye(n);
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end;
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if min(size(Pcol)) == 1
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Pcol = sparse(1:n,Pcol,1,n,n);
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end;
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% Make sure the matrices are sparse and the vector is full.
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if ~issparse(A)
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A = sparse(A);
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end;
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if issparse(b)
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b = full(b);
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end;
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if ~issparse(Pcol)
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Pcol = sparse(Pcol);
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end;
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x = mexlusolve(A,b,Pcol);
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