KSPGetResidualHistory#

Gets the array used to hold the residual history and the number of residuals it contains.

Synopsis#

#include "petscksp.h" 
#include "petscmat.h" 
PetscErrorCode KSPGetResidualHistory(KSP ksp, const PetscReal *a[], PetscInt *na)

Not Collective

Input Parameter#

ksp - iterative context obtained from KSPCreate()

Output Parameters#

a - pointer to array to hold history (or NULL)
na - number of used entries in a (or NULL). Note this has different meanings depending on the reset argument to KSPSetResidualHistory()

Note#

This array is borrowed and should not be freed by the caller.

Can only be called after a KSPSetResidualHistory() otherwise a and na are set to NULL and zero

When reset was PETSC_TRUE since a residual is computed before the first iteration, the value of na is generally one more than the value returned with KSPGetIterationNumber().

Some Krylov methods may not compute the final residual norm when convergence is declared because the maximum number of iterations allowed has been reached. In this situation, when reset was PETSC_TRUE, na will then equal the number of iterations reported with KSPGetIterationNumber()

Some Krylov methods (such as KSPSTCG), under certain circumstances, do not compute the final residual norm. In this situation, when reset was PETSC_TRUE, na will then equal the number of iterations reported with KSPGetIterationNumber()

KSPBCGSL does not record the residual norms for the “subiterations” hence the results from KSPGetResidualHistory() and KSPGetIterationNumber() will be different

Fortran Note#

The Fortran version of this routine has a calling sequence

  call KSPGetResidualHistory(KSP ksp, integer na, integer ierr)

note that you have passed a Fortran array into KSPSetResidualHistory() and you need to access the residual values from this Fortran array you provided. Only the na (number of residual norms currently held) is set.

Level#

advanced

Location#

src/ksp/ksp/interface/itfunc.c

Index of all KSP routines
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Index of all manual pages