# dfgmres_check

Checks consistency and correctness of the user defined data.

## Syntax

dfgmres_check(n, x, b, RCI_request, ipar, dpar, tmp)

## Description

The routine dfgmres_check checks consistency and correctness of the parameters to be passed to the solver routine dfgmres. However this operation does not guarantee that the method gives the correct result. It only reduces the chance of making a mistake in the parameters of the method. Advanced users may skip it if they are sure that the correct data is specified in the solver parameters.

### Warning

Users can modify the contents of these arrays after they are passed to the solver routine only if they are sure that the values are correct and consistent. Basic check for correctness and consistency can be done by calling the dfgmres_check routine, but it does not guarantee that the method will work correctly.

Note that lengths of all vectors are assumed to have been defined in a previous call to the dfgmres_init routine.

## Input Parameters

n

  INTEGER. Contains the size of the problem, and the sizes of arrays x and b.

x

  DOUBLE PRECISION array of size n. Contains the initial approximation to the solution vector. Normally it is equal to 0 or to b.

b

  DOUBLE PRECISION array of size n. Contains the right-hand side vector.

## Output Parameters

RCI_request

  INTEGER. Informs about result of work of the routine.

ipar

  INTEGER array of size 128. Refer to the FGMRES Common Parameters.

dpar

  DOUBLE PRECISION array of size 128. Refer to the FGMRES Common Parameters.

tmp

  DOUBLE PRECISION array of size `((2*ipar(15)+1)*n+ipar(15)*ipar(15)+9)/2 + 1)`. Refer to the FGMRES Common Parameters.

## Return Values

RCI_request= 0

  The routine completes task normally.

RCI_request= -1100

  The routine is interrupted, errors occur.

RCI_request= -1001

  The routine returns some warning messages.

RCI_request= -1010

  The routine changes some parameters to make them consistent or correct.

RCI_request= -1011

  The routine returns some warning messages and changes some parameters.

Parent topic: Iterative Sparse Solvers based on Reverse Communication Interface (RCI ISS)