# VecStrideNorm
Computes the norm of subvector of a vector defined by a starting point and a stride. 
## Synopsis
```
#include "petscvec.h" 
PetscErrorCode VecStrideNorm(Vec v, PetscInt start, NormType ntype, PetscReal *nrm)
```
Collective on Vec


## Input Parameters

- ***v -*** the vector
- ***start -*** starting point of the subvector (defined by a stride)
- ***ntype -*** type of norm, one of NORM_1, NORM_2, NORM_INFINITY



## Output Parameter

- ***norm -*** the norm



## Notes
One must call VecSetBlockSize() before this routine to set the stride
information, or use a vector created from a multicomponent DMDA.

If x is the array representing the vector x then this computes the norm
of the array (x[start],x[start+stride],x[start+2*stride], ....)

This is useful for computing, say the norm of the pressure variable when
the pressure is stored (interlaced) with other variables, say density etc.

This will only work if the desire subvector is a stride subvector




## See Also
 `VecNorm()`, `VecStrideGather()`, `VecStrideScatter()`, `VecStrideMin()`, `VecStrideMax()`

## Level
advanced

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

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/vec/tutorials/ex11.c.html">src/vec/vec/tutorials/ex11.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/vec/tutorials/ex11f.F90.html">src/vec/vec/tutorials/ex11f.F90.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/vec/vec/tutorials/ex11f90.F90.html">src/vec/vec/tutorials/ex11f90.F90.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex42.c.html">src/ksp/ksp/tutorials/ex42.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex43.c.html">src/ksp/ksp/tutorials/ex43.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex22.c.html">src/snes/tutorials/ex22.c.html</A><BR>


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