slepc-3.15.2 2021-09-20
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# DSTranslateHarmonic

Computes a translation of the dense system.

### Synopsis

    #include "slepcds.h"
    PetscErrorCode DSTranslateHarmonic(DS ds,PetscScalar tau,PetscReal beta,PetscBool recover,PetscScalar *g,PetscReal *gamma)

Logically Collective on ds

### Input Parameters

| ds | - the direct solver context
| tau | - the translation amount
| beta | - last component of vector b
| recover | - boolean flag to indicate whether to recover or not

### Output Parameters

| g | - the computed vector (optional)
| gamma | - scale factor (optional)

### Notes

This function is intended for use in the context of Krylov methods only. It computes a translation of a Krylov decomposition in order to extract eigenpair approximations by harmonic Rayleigh-Ritz. The matrix is updated as A + g*b' where g = (A-tau*eye(n))'\b and vector b is assumed to be beta*e_n^T.

The gamma factor is defined as sqrt(1+g'*g) and can be interpreted as the factor by which the residual of the Krylov decomposition is scaled.

If the recover flag is activated, the computed translation undoes the translation done previously. In that case, parameter tau is ignored.

Location: src/sys/classes/ds/interface/dsops.c
Index of all DS routines
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