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# SVDTRLanczosSetScale

Sets the scale parameter for the GSVD.

## Synopsis

    #include "slepcsvd.h"
    PetscErrorCode SVDTRLanczosSetScale(SVD svd,PetscReal scale)

Logically Collective

## Input Parameters

- svd - the singular value solver context

- scale - scale parameter

## Options Database Key

- -svd_trlanczos_scale <scale> - scale factor/threshold

## Notes

This parameter is relevant for the GSVD case only. If the parameter is positive, it indicates the scale factor to multiply \(B\) in the stacked matrix \(Z=[A^*,B^*]^*\). If negative, its absolute value is the threshold for automatic scaling. In automatic scaling, whenever the largest approximate generalized singular value (or the inverse of the smallest value, if `SVD_SMALLEST` is used) exceeds the threshold, the computation is restarted with matrix \(B\) scaled by that value.

## See Also

SVD: Singular Value Decomposition, `SVDTRLANCZOS`, `SVDTRLanczosGetScale()`

## Level

advanced

## Location

src/svd/impls/trlanczos/trlanczos.c

## Examples

src/svd/tutorials/ex51.c

## Implementations

SVDTRLanczosSetScale_TRLanczos() in src/svd/impls/trlanczos/trlanczos.c

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