[FLASH-USERS] [EXTERNAL] Re: Adaptive timestep

[Ricker, Paul Milton]

Heh. It's been "on my list" for ten years...

I agree with Ann that elliptic solves are the complicated part, and
with Tomek that load balancing is an issue. If you, processor, are the
chump stuck with a lot of fine blocks with short timesteps, you will
hold everyone else back. Anecdotally this was an issue with Enzo
scaling, though I seem to remember you could ameliorate the problem
somewhat by distributing work level-by-level.

Paul


On Tue, 2019-10-01 at 16:45 +0000, Sean M. Couch wrote:
> Sounds like we have a volunteer! ;)
> 
> Sean
> 
> -------------------------------------------------------------------
> ---
> Sean M. Couch, Ph.D.
> Assistant Professor
> Department of Physics and Astronomy
> Department of Computational Mathematics, Science, and Engineering
> Facility for Rare Isotope Beams
> Michigan State University
> 567 Wilson Rd, 3260 BPS
> East Lansing, MI 48824
> (517) 884-5035 --- couch at pa.msu.edu --- www.pa.msu.edu/~couch
> On Oct 1, 2019, 12:26 PM -0400, Ricker, Paul Milton <
> pmricker at illinois.edu>, wrote:
> > It would be good to come up with a strategy for developing this
> > feature in FLASH 5. It's been a desired feature for a long time,
> > but it has essentially been triaged out of development since it is
> > not easy and not the most urgent feature for most developers'
> > science. The transition to AMReX is a good opportunity to revisit
> > the question of how hard it would be to implement.
> > 
> > I'll just put that on my to-do list... :)
> > 
> > Paul
> > 
> > 
> > Paul M. Ricker
> > Professor of Astronomy
> > University of Illinois
> > 
https://urldefense.proofpoint.com/v2/url?u=http-3A__sipapu.astro.illinois.edu_-7Ericker&d=DwIF-g&c=nE__W8dFE-shTxStwXtp0A&r=ISY2CKBuLFWqkB5oZl4IHg&m=lj-jZJTDS7STng42H_XBYjwacnOdXFEhyIq-zjugt_c&s=Hmtqp-VAO4yuxvTVMT_XbcP5obADLBD1YtgMMXO-Pxg&e=
> > 
> > On October 1, 2019 11:03:41 AM "Messer II, Bronson" <
> > bronson at ornl.gov> wrote:
> > 
> > > Hi Sean, Matuesz, et al.,
> > > 
> > > Sean is right both about not having sub-cycling in the current
> > > solvers and about the desire to change that in the future for
> > > FLASH5.
> > > 
> > > So, I guess I didn’t have a different opinion at all, just felt
> > > the need to chime in. :)
> > > 
> > > Bronson
> > > 
> > > > On Oct 1, 2019, at 11:33 AM, Sean M. Couch <couch at pa.msu.edu>
> > > > wrote:
> > > > 
> > > > Hi Mateusz,
> > > > 
> > > > I will venture my view of this and others can chime in if they
> > > > have a different opinion. Also, I’m assuming by adaptive
> > > > timestep you mean sub-cycling in time where different
> > > > refinement levels take different time steps?
> > > > 
> > > > For FLASH5, we are transitioning to the AMReX package. AMReX is
> > > > built on the idea of time sub-cycling so in principle, we could
> > > > utilize that. For that matter, PARAMESH was also built to allow
> > > > time sub-cycling, we just never used it. As of now, for the
> > > > solvers we are porting to FLASH5/AMReX we are still making the
> > > > assumption of a single global time step. This simplifies things
> > > > considerably. But I am of the opinion that, eventually, we
> > > > should implement time sub-cycling and take advantage of what
> > > > AMReX offers in that regard. This, however, will not likely be
> > > > a feature available from the outset.
> > > > 
> > > > Now, what might speed things along is capable developers
> > > > willing to lend a hand in the implementation ;)
> > > > 
> > > > Sean
> > > > 
> > > > -------------------------------------------------------------
> > > > ---------
> > > > Sean M. Couch, Ph.D.
> > > > Assistant Professor
> > > > Department of Physics and Astronomy
> > > > Department of Computational Mathematics, Science, and
> > > > Engineering
> > > > Facility for Rare Isotope Beams
> > > > Michigan State University
> > > > 567 Wilson Rd, 3260 BPS
> > > > East Lansing, MI 48824
> > > > (517) 884-5035 --- couch at pa.msu.edu --- 
> > > > http://www.pa.msu.edu/~couch
> > > > On Sep 30, 2019, 7:55 PM -0400, Mateusz Ruszkowski <
> > > > mateuszr at umich.edu>, wrote:
> > > > > 
> > > > > 
> > > > > 
> > > > > Hi all,
> > > > > 
> > > > > 
> > > > > Does anyone know if there a plan to extend FLASH to include
> > > > > adaptive timestep or if users would be interested in such a
> > > > > code feature?
> > > > > Myself and a number of my collaborators would definitely be
> > > > > interested in using such a code capability.
> > > > > 
> > > > > 
> > > > > Cheers,
> > > > > Mateusz
> >  
-- 
Paul M. Ricker
Professor of Astronomy
University of Illinois
http://sipapu.astro.illinois.edu/~ricker