# 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>


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[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](/docs/manualpages/index.md)  
[Index of all manual pages](/docs/manualpages/singleindex.md)  
