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Справка Scilab >> Sparse Matrix > Sparse Decompositions > luget

luget

extraction of sparse LU factors

Calling Sequence

[P,L,U,Q]=luget(hand)

Arguments

hand

handle, output of lufact

P

sparse permutation matrix

L

sparse matrix, lower triangular if hand is obtained from a non singular 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(hand) with hand obtained by the command [hand,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.

Examples

a=rand(5,2)*rand(2,5);A=sparse(a);
[hand,rk]=lufact(A);[P,L,U,Q]=luget(hand);
full(L), P*L*U*Q-A
clean(P*L*U*Q-A)
ludel(hand)

See Also

  • sparse — sparse matrix definition
  • lusolve — sparse linear system solver
  • luget — extraction of sparse LU factors
  • clean — очищает матрицы (округление малых значений до нуля)
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Last updated:
Thu Oct 02 14:01:07 CEST 2014