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lufact(G) Scilab Function lufact(G)
NAME
luget - sparse lu factorization
CALLING SEQUENCE
[P,L,U,Q]=luget(ptr)
PARAMETERS
ptr : pointer, output of lufact
P : sparse permutation matrix
L : sparse matrix, lower triangular if ptr is obtained from a non singu-
lar matrix
U : square non singular upper triangular sparse matrix with ones along
the main diagonal
Q : sparse permutation matrix
DESCRIPTION
[P,L,U,Q]=luget(ptr) with ptr obtained by the command [ptr,rk]=lufact(A)
with A a sparse matrix returns four sparse matrices such that P*L*U*Q=A.
The A matrix needs not be full rank but must be square (since A is assumed
sparse one may add zeros if necessary to squaring down A).
If A is singular, the L matrix is column compressed (with rk independent
nonzero columns): the nonsingular sparse matrix Q'*inv(U) column
compresses A.
EXAMPLE
a=rand(5,2)*rand(2,5);A=sparse(a);
[ptr,rk]=lufact(A);[P,L,U,Q]=luget(ptr);
full(L), P*L*U*Q-A
clean(P*L*U*Q-A)
ludel(ptr)
SEE ALSO
sparse, lusolve, luget, clean
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