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# luget

extraction of sparse LU factors

### Syntax

[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`

.

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