# [petsc-users] Can I use TS routines for operator split formulation

Barry Smith bsmith at mcs.anl.gov
Mon Jun 9 13:47:38 CDT 2014

```On Jun 9, 2014, at 1:37 PM, Shriram Srinivasan <shriram at ualberta.ca> wrote:

> It isnt an ODE actually. Its the unsteady diffusion equation u_t + div(k grad(u)) = f. The matrices A and B represent discretisations of the fluxes.  I am using operator splitting to advance the solution in two stages in every time step:
> First compute u*, then use it to compute u.

Understood. But if you can define/describe the exact operator split method (i.e. what defines A and B) then we see how it could possibly be handled within TS.

Our goal is, when possible, to make TS flexible enough to support some operator split methods, we can only do this by specific examples.

Thanks

Barry

>
> Shriram
>
>
>
> On 14-06-09 12:28 PM, Barry Smith wrote:
>>   What is the ODE you are solving?
>>
>>    Barr
>>
>> On Jun 9, 2014, at 11:51 AM, Shriram Srinivasan <shriram at ualberta.ca> wrote:
>>
>>> Hi,
>>> I am working with the (discretised) PDE:
>>> (u* - u_prev) + (tau )A u* = f1
>>> (u - u*) + (tau)B u = f2
>>> Here A and B are constant matrices which have been assembled, u_prev is solution at previous time level, tau is the time step and u is the solution at current time level.
>>>
>>> It appears to me I cannot rewrite this in a form required by the TS module. So my question(s) are:
>>>
>>> 1) Am I missing something here, or is there a way to cast this into the framework of TS
>>> 2) If there isn’t a way, am I better off doing the time stepping myself ?
>>>
>>> Thanks,
>>> Shriram
>

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