luget

Scilab Function
Last update : April 1993

luget - extraction of sparse LU factors

### Calling Sequence

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

### Parameters

- `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` , `lusolve` , `luget` , `clean` ,