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# umf_lusolve

solve a linear sparse system given the LU factors

### Syntax

[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 language: 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 conjunction 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 proceeded (as in umfpack) to
give a better numerical solution.

### Examples

see the example section of umf_lufact

### See also

- umfpack — solve sparse linear system
- umf_lufact — lu factorization of a sparse matrix
- umf_luget — retrieve lu factors at the Scilab level
- umf_ludel — utility function used with umf_lufact
- umf_luinfo — get information on LU factors

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