[MITgcm-support] optim_m1qn3: maximum iterations reached?

[Martin Losch]

Hi Dan,

thanks for using this routine. Do you think that we can reproduce this somewhat odd behavior with a simple optimization (i.e. with a cheap costfunction like the “testbed” in optim_m1qn3)?

nsim = numter*nfunc should not change during the optimization, only at the (successful) end, it is overwritten somewhere in m1qn3a or so to store the actual number of simulations. So my only guess is that you (accidentally) restart the optimization (with modified parameters) after m1qn3 thinks it’s over?

Maybe it would be helpful to have look at the output of optim_m1qn3, but also of m1qn3 itself (if you didn’t change it: fname_m1qn3='output_m1qn3.txt’), but also at the calling seqence (script). Depending on the size, you can send it directly to me.

Martin

> On 24. Sep 2020, at 09:26, Daniel Goldberg <dan.goldberg at ed.ac.uk> wrote:
> 
> Hi Martin
> 
> I am using optim_m1qn3 (installed from your github repo).
> 
> I have been using it in optimisations with data.optim parameters as follows:
> 
>  &OPTIM
>  optimcycle=0,
>  numiter=1000,
>  nfunc=10,
>  dfminfrac=0.001,
>  iprint=10,
>  nupdate=5,
>  /
> 
> and am seeing the optimisation terminate with omode=5 after about 100 iterations. The manual for m1qn3 suggests the maximum number of simulations has been reached, which is a lot less than numiter*nfunc, which (according to the git readme) is the max number of simulations. (Though i do note that "nsim" in the text output from the optim_m1qn3 executable changes at some point in the optimisation from its initial value of 10000.) 
> 
> I then ran the optimisation again with nfunc=20 to see what would happen -- this time there is a termination with omode=4, the maximum number of iterations being reached -- this happened at optimcycle=116. Here, i notice that each subsequent optimcycle gives omode=1 in the optim_m1qn3 output -- im not sure if this is significant. 
> 
> I was wondering if this behaviour makes sense to you, and if you would be able to explain it? Happy to provide more output from optim_m1qn3 (from the more recent optimisation with nfunc=20; the previous nfunc=10 output is deleted).
> 
> Many thanks
> Dan
> 
> -- 
> --- PLEASE NOTE THAT I AM CURRENTLY WORKING FROM HOME AS A MEASURE OF SOCIAL DISTANCING DURING THE COVID-19 PANDEMIC ---
> 
> Daniel Goldberg, PhD
> Reader in Glaciology
> School of Geosciences, University of Edinburgh
> Geography Building, Drummond Street, Edinburgh EH8 9XP
> 
> 
> em: dan.goldberg at ed.ac.uk
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