dcg

Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

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ID 766686

Date 3/22/2024

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dcg

Computes the approximate solution vector.

Syntax

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

Include Files

Fortran: mkl_rci.fi, mkl_rci.f90

Description

The dcg routine computes the approximate solution vector using the CG method [Young71]. The routine dcg uses the vector in the array x before the first call as an initial approximation to the solution. The parameter RCI_request gives you information about the task completion and requests results of certain operations that are required by the solver.

Note that lengths of all vectors must be defined in a previous call to the dcg_init routine.

Input Parameters

n: INTEGER. Sets the size of the problem.
x: DOUBLE PRECISION . Array of size n. Contains the initial approximation to the solution vector.
b: DOUBLE PRECISION . Array of size n. Contains the right-hand side vector.
tmp: DOUBLE PRECISION . Array of size (n, 4). 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. Contains the updated approximation to the solution vector.
ipar: INTEGER . Array of size 128. Refer to the CG Common Parameters.
dpar: DOUBLE PRECISION . Array of size 128. Refer to the CG Common Parameters.
tmp: DOUBLE PRECISION . Array of size (n,4). 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 you request both tests.
RCI_request=-2: Indicates that 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.

Parent topic: RCI ISS Routines

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