# KSPComputeEigenvaluesExplicitly

Computes all of the eigenvalues of the preconditioned operator using LAPACK.

### Synopsis

    #include "petscksp.h"
    PetscErrorCode PETSCKSP_DLLEXPORT KSPComputeEigenvaluesExplicitly(KSP ksp,PetscInt nmax,PetscReal *r,PetscReal *c)

Collective on KSP

### Input Parameter

| ksp | - iterative context obtained from KSPCreate()
| n | - size of arrays r and c

### Output Parameters

| r | - real part of computed eigenvalues
| c | - complex part of computed eigenvalues

### Notes

This approach is very slow but will generally provide accurate eigenvalue estimates. This routine explicitly forms a dense matrix representing the preconditioned operator, and thus will run only for relatively small problems, say n < 500.

Many users may just want to use the monitoring routine KSPMonitorSingularValue() (which can be set with option -ksp_monitor_singular_value) to print the singular values at each iteration of the linear solve.

The preconditoner operator, rhs vector, solution vectors should be set before this routine is called. i.e use KSPSetOperators(),KSPSolve() or KSPSetOperators()

### Keywords

KSP, compute, eigenvalues, explicitly

### See Also

KSPComputeEigenvalues(), KSPMonitorSingularValue(), KSPComputeExtremeSingularValues(), KSPSetOperators(), KSPSolve()

Level:advanced
Location:src/ksp/ksp/interface/eige.c
Index of all KSP routines
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Index of all manual pages