PETSc version 3.17.0
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# KSPChebyshevSetEigenvalues

Sets estimates for the extreme eigenvalues of the preconditioned problem.

### Synopsis

    #include "petscksp.h"
    PetscErrorCode  KSPChebyshevSetEigenvalues(KSP ksp,PetscReal emax,PetscReal emin)

Logically Collective on ksp

### Input Parameters

| ksp | - the Krylov space context
| emax, emin | - the eigenvalue estimates

### Options Database

| -ksp_chebyshev_eigenvalues emin,emax | - extreme eigenvalues

### Note

Call KSPChebyshevEstEigSet() or use the option -ksp_chebyshev_esteig a,b,c,d to have the KSP estimate the eigenvalues and use these estimated values automatically.

When KSPCHEBYSHEV is used as a smoother, one often wants to target a portion of the spectrum rather than the entire spectrum. This function takes the range of target eigenvalues for Chebyshev, which will often slightly over-estimate the largest eigenvalue of the actual operator (for safety) and greatly overestimate the smallest eigenvalue to improve the smoothing properties of Chebyshev iteration on the higher frequencies in the spectrum.

### See Also

KSPChebyshevEstEigSet()

### Level

intermediate

### Location

src/ksp/ksp/impls/cheby/cheby.c

### Implementations

KSPChebyshevSetEigenvalues_Chebyshev in src/ksp/ksp/impls/cheby/cheby.c
Index of all KSP routines
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