# KSPMonitorSingularValue#

Prints the two norm of the true residual and estimation of the extreme singular values of the preconditioned problem at each iteration.

## Synopsis#

#include "petscksp.h"
PetscErrorCode KSPMonitorSingularValue(KSP ksp, PetscInt n, PetscReal rnorm, PetscViewerAndFormat *vf)


Logically Collective

## Input Parameters#

• ksp - the iterative context

• n - the iteration

• rnorm - the two norm of the residual

• vf - The viewer context

## Options Database Key#

• -ksp_monitor_singular_value - Activates KSPMonitorSingularValue()

## Notes#

The KSPCG solver uses the Lanczos technique for eigenvalue computation, while KSPGMRES uses the Arnoldi technique; other iterative methods do not currently compute singular values.

This is not called directly by users, rather one calls KSPMonitorSet(), with this function as an argument, to cause the monitor to be used during the KSP solve.

Call KSPMonitorSingularValueCreate() to create the context needed by this monitor

KSP: Linear System Solvers, KSP, KSPMonitorSet(), KSPComputeExtremeSingularValues(), KSPMonitorSingularValueCreate()

intermediate

## Location#

src/ksp/ksp/interface/iterativ.c

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