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# TSSetComputeExactError
Set the function used to automatically compute the exact error for the timestepping. 
## Synopsis
```
#include "petscts.h"  
PetscErrorCode TSSetComputeExactError(TS ts, PetscErrorCode (*exactError)(TS, Vec, Vec))
```
Logically collective


## Input Parameters

- ***ts -*** time stepping context
- ***exactError -*** The function which computes the solution error



## Calling sequence of `exactError`
```none
PetscErrorCode exactError(TS ts, Vec u)
```

- ***ts -*** The timestepping context
- ***u  -*** The approximate solution vector
- ***e  -*** The  vector in which the error is stored





## See Also
 [](ch_ts), `TS`, `TSGetComputeExactError()`, `TSComputeExactError()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ts/interface/ts.c.html#TSSetComputeExactError">src/ts/interface/ts.c</A>

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ts/tutorials/ex77.c.html">src/ts/tutorials/ex77.c</A><BR>


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