:orphan:
# VecNormBegin
Starts a split phase norm computation. 
## Synopsis
```
#include "petscvec.h"    
PetscErrorCode VecNormBegin(Vec x, NormType ntype, PetscReal *result)
```

## Input Parameters

- ***x -*** the first vector
- ***ntype -*** norm type, one of `NORM_1`, `NORM_2`, `NORM_MAX`, `NORM_1_AND_2`
- ***result -*** where the result will go (can be `NULL`)





## Notes
Each call to `VecNormBegin()` should be paired with a call to `VecNormEnd()`.


## See Also
 `VecNormEnd()`, `VecNorm()`, `VecDot()`, `VecMDot()`, `VecDotBegin()`, `VecDotEnd()`, `PetscCommSplitReductionBegin()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/vec/utils/comb.c.html#VecNormBegin">src/vec/vec/utils/comb.c</A>


---
[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/vec/vec/utils/comb.c)


[Index of all Vec routines](index.md)  
[Table of Contents for all manual pages](/manualpages/index.md)  
[Index of all manual pages](/manualpages/singleindex.md)