:orphan:
# TSSetTransientVariable
sets function to transform from state to transient variables 
## Synopsis
```
#include "petscts.h"  
PetscErrorCode TSSetTransientVariable(TS ts, TSTransientVariable tvar, void *ctx)
```
Logically Collective


## Input Parameters

- ***ts -*** time stepping context on which to change the transient variable
- ***tvar -*** a function that transforms to transient variables
- ***ctx -*** a context for tvar



## Calling sequence of `tvar`
```none
PetscErrorCode tvar(TS ts, Vec p, Vec c, void *ctx)
```

- ***ts -*** timestep context
- ***p -*** input vector (primitive form)
- ***c -*** output vector, transient variables (conservative form)
- ***ctx -*** [optional] user-defined function context





## Notes
This is typically used to transform from primitive to conservative variables so that a time integrator (e.g., `TSBDF`)
can be conservative.  In this context, primitive variables P are used to model the state (e.g., because they lead to
well-conditioned formulations even in limiting cases such as low-Mach or zero porosity).  The transient variable is
C(P), specified by calling this function.  An IFunction thus receives arguments (P, Cdot) and the IJacobian must be
evaluated via the chain rule, as in
```none
     dF/dP + shift * dF/dCdot dC/dP.
```



## See Also
 [](ch_ts), `TS`, `TSBDF`, `DMTSSetTransientVariable()`, `DMTSGetTransientVariable()`, `TSSetIFunction()`, `TSSetIJacobian()`

## Level
advanced

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


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