# PCGAMGSetThresholdScale
Relative threshold reduction at each level 
## Synopsis
```
#include "petscpc.h" 
#include "petscksp.h" 
PetscErrorCode PCGAMGSetThresholdScale(PC pc, PetscReal v)
```
Not collective


## Input Parameters

- ***pc -*** the preconditioner context
- ***scale -*** the threshold value reduction, usually < 1.0



## Options Database Key

- ***-pc_gamg_threshold_scale <v> -*** set the relative threshold reduction on each level



## Note
The initial threshold (for an arbitrary number of levels starting from the finest) can be set with `PCGAMGSetThreshold()`.
This scaling is used for each subsequent coarsening, but must be called before `PCGAMGSetThreshold()`.




## See Also
 `PCGAMG`, `PCGAMGSetThreshold()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/gamg/gamg.c.html#PCGAMGSetThresholdScale">src/ksp/pc/impls/gamg/gamg.c</A>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/gamg/gamg.c.html#PCGAMGSetThresholdScale_GAMG">PCGAMGSetThresholdScale_GAMG in src/ksp/pc/impls/gamg/gamg.c</A><BR>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/ksp/pc/impls/gamg/gamg.c)


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