# umf_lusolve

solve a linear sparse system given the LU factors

## Calling Sequence

    [x] = umf_lusolve(LU_ptr, b [, st, A])

## Arguments

LU_ptr

  a pointer to umf lu factors (L,U,p,q,R)

b

  a real or complex column vector or a matrix (multiple rhs)

st

  (optional) a string "Ax=b" (default) or "Ax'=b" (to be written "Ax''=b" in scilab langage: a quote in a string must be doubled !)

A

  (optional) the sparse square matrix corresponding to the LU factors (LU_ptr must be got with LU_ptr = umf_lufact(A))

x

  a column vector or a matrix in case of multiple rhs ( x(:,i) is solution of A x(:,i) = b(:,i) or A'x(:,i) = b(:,i) )

## Description

This function must be used in conjonction with umf_lufact which computes the LU factors of a sparse matrix. The optional `st` argument lets us choose between the solving of Ax=b (general case) or of A'x=b (sometimes useful). If you give the 4th argument then iterative refinement will be also proceceed (as in umfpack) to give a better numerical solution.

## Examples

see the example section of umf_lufact

## See Also

- umfpack
- umf_lufact
- umf_luget
- umf_ludel
- umf_luinfo