[MITgcm-devel] seaice adjoint and EVP

[Martin Losch]

OK, I will go back to something more stable and fix the bug in ocean  
stress at the same time. This will require new output.txt files for  
lab sea (and adjoint, the latter I will leave to you).

Jean-Michel, can I do these changes now or would like me to wait a  
little longer?

Martin

On 15 May 2007, at 13:34, Patrick Heimbach wrote:

>
> Hi Martin,
>
> I'm happy whichever way you change, as long as it is ensured
> that expression under sqrt() strictly > 0.
> Simplest seems to be just SQRT(deltaC+SEAICE_EPS_SQ)
>
> Re the (e11c-e22C) term, it might indeed be unwise
> to substract 2 large numbers if it can be avoided.
>
> Cheers
> -Patrick
>
>
>
> On May 15, 2007, at 3:40 AM, Martin Losch wrote:
>
>> 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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>>>> MITgcm-devel at mitgcm.org
>>>> http://mitgcm.org/mailman/listinfo/mitgcm-devel
>>>
>>> ---
>>> 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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>>
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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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