[petsc-dev] BDF implementation

[Abhyankar, Shrirang G.]

-----Original Message-----
From: Lisandro Dalcin <dalcinl at gmail.com>
Date: Wednesday, March 30, 2016 at 4:00 PM
To: "Zhang, Hong" <hongzhang at anl.gov>
Cc: Jed Brown <jed at jedbrown.org>, petsc-dev mailing list
<petsc-dev at mcs.anl.gov>, Shri <abhyshr at anl.gov>
Subject: Re: [petsc-dev] BDF implementation

>On 30 March 2016 at 18:50, Hong Zhang <hongzhang at anl.gov> wrote:
>> If there are state changes in the post event callback, then multistep
>>methods would not be a good choice for the application.
>> I would use multistage methods such as RK type instead.
>>
>
>It all depends on the frequency of events respect to the timestep.
>
>> However, restarting the time stepper may still be necessary for other
>>types of discontinuities, e.g. changes in the RHS function.
>
>Oh! Very good point. Then, the only way to know is the postevent
>callback flagging the timestepper about it.

The restart will only work when TSEvent is used. What about without
TSEvent?

>Well, A
>VecGetArray()/RestoreArray() on the solution would still work, even if
>the postevent callback does not actually modify the state. However,
>this is sounds like a bad API for users to flag the restart.

How about an additional check on RHS function vector state, similar to
what¹s been done with the solution vector state?


>> So I would suggest to do unconditional restart at discontinuity points
>>for safety.
>>
>
>So ARKIMEX has to be fixed. Unless we agree and document that
>VecGetArray()/RestoreArray() is the way to flag discontinuities in the
>RHS function.
>
>
>-- 
>Lisandro Dalcin
>============
>Research Scientist
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>Extreme Computing Research Center (ECRC)
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