# Subroutine mld_precaply
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Subroutine mld_precaply

`mld_precaply(p,x,y,desc_a,info)`
`mld_precaply(p,x,y,desc_a,info,trans,work)`

This routine computes , where is a previously built preconditioner, stored into `p`, and denotes the preconditioner itself or its transpose, according to the value of `trans`. Note that, when MLD2P4 is used with a Krylov solver from PSBLAS, `mld_precaply` is called within the PSBLAS routine `psb_krylov` and hence it is completely transparent to the user.

Arguments

`p` | `type(mld_`x `prec_type), intent(inout)`.
| The preconditioner data structure, containing the local part of . Note that x must be chosen according to the real/complex, single/double precision version of MLD2P4 under use.
`x` | type`(`kind_parameter`), dimension(:), intent(in)`.
| The local part of the vector . Note that type and kind_parameter must be chosen according to the real/complex, single/double precision version of MLD2P4 under use.
`y` | type`(`kind_parameter`), dimension(:), intent(out)`.
| The local part of the vector . Note that type and kind_parameter must be chosen according to the real/complex, single/double precision version of MLD2P4 under use.
`desc_a` | `type(psb_desc_type), intent(in)`.
| The communication descriptor associated to the matrix to be preconditioned.
`info` | `integer, intent(out)`.
| Error code. If no error, 0 is returned. See Section 7 for details.
`trans` | `character(len=1), optional, intent(in).`
| If `trans` = `'N','n'` then ; if `trans` = `'T','t'` then (transpose of ; if `trans` = `'C','c'` then (conjugate transpose of .
`work` | type`(`kind_parameter`), dimension(:), optional, target`.
| Workspace. Its size should be at least `4 * psb_cd_get_local_` `cols(desc_a)` (see the PSBLAS User's Guide). Note that type and kind_parameter must be chosen according to the real/complex, single/double precision version of MLD2P4 under use.

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