[MITgcm-support] run speed unaffected by timestep, 'deltaT', in?

[Jonny Williams]

Hi Dimitris

That's great, thanks very much indeed.

Just to give you some background on this, I had been having trouble running
my version of the MITgcm with the full depth profile, which meant that I
was unable to run with my standard timestep of 2400s for a
latitude-longitude grid spacing of 1x1 degree. I have found that I only
need to do a fairly short spinup with a much reduced timestep to remove
early transient noise.

I'm currently out of run time allocation on our machine but am now in a
good position to hit the ground running with this when I have some more!

Thanks again

Jonny




On 19 May 2014 18:37, Dimitris Menemenlis <dmenemenlis at gmail.com> wrote:

> What horizontal grid spacing are you using?
>
> To give you some idea of a typical spin-up progression for deltat,
> for the 1/12-deg global (llc1080) simulation, I integrated for:
> - 1 day with deltat = 30 s,
> - 9 days with deltat = 90 s,
> - 10 days with deltat = 120 s,
> - 25 days with deltat = 180 s,
> - then starting on day 45 set deltat = 240 s.
>
> The key diagnostic to look at in STDOUT is adcfl*.
> If they consistently fall below 0.5, then you can increase deltat.
>
> Regarding integration times, as Liam suggested, the overall time
> may be dominated by parts of code that do not depend on deltat.
> So go to end of STDOUT and find out where your code is spending time.
>
> On May 19, 2014, at 4:30 AM, Jonny Williams <Jonny.Williams at bristol.ac.uk>
> wrote:
>
> Hi again
>
> Regarding this, it seems that I do actually get a speed up of
> approximately 10 times from a factor of 100 difference in the timestep. Is
> this roughly what people would expect?
>
> Thanks again and sorry for the initial confusion!
>
> Jonny
>
> On 19 May 2014 12:17, Jonny Williams <Jonny.Williams at bristol.ac.uk> wrote:
>
>> Hi there
>>
>> I am currently running a regional version of the MIgcm with OBCS and EXF
>> forcing packages turned on. For the initial few years of the run I am
>> running with a very short timestep of 24s and then after that I am running
>> with a much linger timestep, 2400s.
>>
>> I was expecting a significant increased in run speed but this has not
>> happened. I am recompiling in between these run steps.
>>
>
>
> _______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mitgcm.org/mailman/listinfo/mitgcm-support
>
>


-- 
Dr Jonny Williams
School of Geographical Sciences
University of Bristol
University Road
BS8 1SS

+44 (0)117 3318352
jonny.williams at bristol.ac.uk
bit.ly/jonnywilliams
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mitgcm.org/pipermail/mitgcm-support/attachments/20140520/3bcf69c9/attachment.htm>