[MITgcm-devel] seaice adjoint and EVP

[Martin Losch]

Hi Patrick,

the lines in question are:
             deltaC = (e11C+e22C)**2 + (e11C-e22C)**2 *recip_ecc2
      &           + 4. _d 0*recip_ecc2*e12C**2
             deltaC = MAX(SQRT(deltaC),SEAICE_EPS)
             deltaZ = (e11Z+e22Z)**2 + (e11Z-e22Z)**2 *recip_ecc2
      &           + 4. _d 0*recip_ecc2*e12Z**2
             deltaZ = MAX(SQRT(deltaZ),SEAICE_EPS)

Previously it was deltaC = SQRT(MAX(deltaC,SEAICE_EPS_SQ)), which as   
far as I remember made the code very sensitive (O(SEAICE_EPS_SQ)) I  
was hoping to reduce this sensitivity to O(SEAICE_EPS), and made sure  
that in the expression for deltaC it is clear that it cannot become  
negative, obviously I forgot zero). I am equally happy with the  
former and/or your suggestion deltaC = SQRT(deltaC+SEAICE_EPS_SQ).

If fact, I am no longer sure that this expressioin (e11C-e22C) is  
clever at all, as I am substracting potentially large numbers from  
each other (du/dx-dv/dy)?

Let's change it back to the "original", but since it changes the  
results, why not do it together with the bug-fix in  
seaice_ocean_stress.F, which changes the results even more?

Martin

On 15 May 2007, at 04:19, Patrick Heimbach wrote:

>
> Hi again,
>
> an update.
> The exf_check_range problem was a different issue.
>
> So, I suggest for seaice_evp to either revert to previous
> SQRT(MAX(deltaC,SEAICE_EPS))
> or to simply
> SQRT(deltaC+SEAICE_EPS)
>
> (same for deltaZ)
>
> -Patrick
>
>
>
> On May 14, 2007, at 7:53 PM, Patrick Heimbach wrote:
>
>>
>> Hi Martin,
>>
>> it's not clear why in seaice_evp.F (revision 1.8)
>> you changed a sqrt expression that could never become zero
>> to one that can. Your comment in CVS log:
>>
>> - replace SQRT(MAX(deltaC,SEAICE_EPS)) by MAX(SQRT 
>> (deltaC),SEAICE_EPS)
>>   help the adjoint (this also changes the results slightly)
>>
>> actually does the opposite (produces NAN's).
>>
>> Problem is that when I revert to old expression I get a stop in
>> exf_check_range.F
>>
>> So at least two things seem wrong in recent seaice_evp.F
>>
>> -Patrick
>>
>> ---
>> Dr Patrick Heimbach | heimbach at mit.edu | http://www.mit.edu/~heimbach
>> MIT | EAPS, 54-1518 | 77 Massachusetts Ave | Cambridge, MA 02139, USA
>> FON: +1-617-253-5259 | FAX: +1-617-253-4464 | SKYPE: patrick.heimbach
>>
>>
>> _______________________________________________
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>
> ---
> Dr Patrick Heimbach | heimbach at mit.edu | http://www.mit.edu/~heimbach
> MIT | EAPS, 54-1518 | 77 Massachusetts Ave | Cambridge, MA 02139, USA
> FON: +1-617-253-5259 | FAX: +1-617-253-4464 | SKYPE: patrick.heimbach
>
>
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