Developer Reference

  • 2020.2
  • 07/15/2020
  • Public Content
Contents

dcgmrhs

Computes the approximate solution vectors.

Syntax

dcgmrhs
(
n
,
x
,
nrhs
,
b
,
RCI_request
,
ipar
,
dpar
,
tmp
)
Include Files
  • Fortran:
    mkl_rci.fi
    ,
    mkl_rci.f90
Description
The routine
dcgmrhs
computes approximate solution vectors using the CG with multiple right-hand sides (MRHS) method [Young71]. The routine
dcgmrhs
uses the value that was in the
x
before the first call as an initial approximation to the solution. The parameter
RCI_request
gives information about task completion status and requests results of certain operations that are required by the solver.
Note that lengths of all vectors are assumed to have been defined in a previous call to the
dcgmrhs_init
routine.
Input Parameters
n
INTEGER
.
Sets the size of the problem, and the sizes of arrays
x
and
b
.
x
DOUBLE PRECISION
.
Array of size
n
*
nrhs
. Contains the initial approximation to the solution vectors.
nrhs
INTEGER
.
Sets the number of right-hand sides.
b
DOUBLE PRECISION
.
Array of size
n
*
nrhs
. Contains the right-hand side vectors.
tmp
DOUBLE PRECISION
.
Array of size
(
n
, 3+
nrhs
)
. Refer to the CG Common Parameters.
Output Parameters
RCI_request
INTEGER
.
Gives information about result of work of the routine.
x
DOUBLE PRECISION
.
Array of size
(
n
by
nrhs
)
. Contains the updated approximation to the solution vectors.
ipar
INTEGER
.
Array of size
(128+2*
nrhs
)
. Refer to the CG Common Parameters.
dpar
DOUBLE PRECISION
.
Array of size
(128+2*
nrhs
)
. Refer to the CG Common Parameters.
tmp
DOUBLE PRECISION
.
Array of size
(
n
,
(3+
nrhs
))
. Refer to the CG Common Parameters.
Return Values
RCI_request
=0
Indicates that the task completed normally and the solution is found and stored in the vector
x
. This occurs only if the stopping tests are fully automatic. For the user defined stopping tests, see the description of the
RCI_request
= 2
.
RCI_request
=-1
Indicates that the routine was interrupted because the maximum number of iterations was reached, but the relative stopping criterion was not met. This situation occurs only if both tests are requested by the user.
RCI_request
=-2
The routine was interrupted because of an attempt to divide by zero. This situation happens if the matrix is non-positive definite or almost non-positive definite.
RCI_request
=- 10
Indicates that the routine was interrupted because the residual norm is invalid. This usually happens because the value
dpar
(6)
was altered outside of the routine, or the
dcg_check
routine was not called.
RCI_request
=-11
Indicates that the routine was interrupted because it enters the infinite cycle. This usually happens because the values
ipar
(8)
,
ipar
(9)
,
ipar
(10)
were altered outside of the routine, or the
dcg_check
routine was not called.
RCI_request
= 1
Indicates that you must multiply the matrix by
tmp
(1:
n
,1)
, put the result in the
tmp
(1:
n
,2)
, and return control back to the routine
dcg
.
RCI_request
= 2
Indicates that you must perform the stopping tests. If they fail, return control back to the
dcg
routine. Otherwise, the solution is found and stored in the vector
x
.
RCI_request
= 3
Indicates that you must apply the preconditioner to
tmp
(:, 3)
, put the result in the
tmp
(:, 4)
, and return control back to the routine
dcg
.