[MITgcm-devel] optim_numbmod: parameters in data.optim

[Martin Losch]

Hi Holly,

dfmin was somewhat inspired from m1qn3 (<http://www-roc.inria.fr/~gilbert/modulopt/optimization-routines/m1qn3/m1qn3.html>, lsopt's successor, which I used a lot before I was sucked into the MITgcm-affairs. However, I just realized that the parameter there is called df1 and is the absolute expected decrease. So maybe a better name would be dfcFrac or so? 

Anyway, no-one else seems to be too excited about it? And using shell scripts to set fmin in data.optim is an obvious solution that I didn't even think about ...

Martin

On Mar 27, 2012, at 11:58 AM, Holly Dail wrote:

> Martin -
> 
> I can't speak to your question about ff, but I did want to say this seems like a great idea to me (assuming there is no technical issue).  Like many perhaps, I have a script that does this automatically, but floating point math isn't so obvious in shell scripts so this option would be helpful for many.
> 
> Would it be more intuitive to specify the converse -- 90% instead of 10% (could call it fminFrac or fminPct).  That would fit better with the current fmin construct.
> 
> Holly
> 
> On Mar 27, 2012, at Mar 27 , 4:22 AM, Martin Losch wrote:
> 
>> Hi there,
>> 
>> I would like to add a new parameter to data.optim.
>> Rather than specifying the expected optimized cost function value "fmin", I'd like to be able to specify a relative reduction, i.e. have something like dfmin = 0.1 for an expected decrease of 10%. This, to my mind, is much easier to do, especially, if you look at a series of optimization runs, where the initial cost function value is different between experiments by orders of  magnitude. Don't worry, fmin, will still be there and usable, I just want to add this option.
>> 
>> Now, for this to work I need the cost function value as computed by the model. This value is both in ecco_cost_* and ecco_ctrl_*, and it's read by optim_readdata.F (fileff), and optim_readdata is called from optim_numbmod, which would give me an easy way of computed fmin=(1-dfmin)*ff.
>> But unfortunately only for the "costname"-file, ff is returned as ff=fileff, for the ctrlname-file ff=0. I was wondering, if this is really necessary, or whether I can just return ff=fileff each time optim_readdata is called. I could also choose to return it whenever lheaderonly=.true. (as it is the case when called from optim_numbmod). I have the impression, from the output of optim.x, that neither of these changes, changes the output. Would you expect any changes in the results if ff=fileff is returned to optim_numbmod?
>> 
>> Martin
>> 
>> 
>> 
>> 
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> 
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