[MITgcm-support] zonal or meridional means on multiple processors

[Samar Khatiwala]

Hi Martin

I don't have an implementation in the MITgcm context.

The link JM just sent does what you want but (I think) requires  
multiple MPI calls. The implementation I had in
mind requires a single call. But the former will save you (or at  
least postpone) the pain of learning MPI.

Samar

On Jan 17, 2008, at 10:53 AM, Martin Losch wrote:

> Hi Samar,
> thanks, but it does mean that I'll have to use MPI - routines  
> directly, something I usually don't do (I know it's embarrassing,  
> that I don't even know the basic). Do you have by any chance the  
> code snippet with MPI_Gather in the MITgcm context?
>
> Martin
> On 17 Jan 2008, at 15:12, Samar Khatiwala wrote:
>
>> Hi Martin
>>
>> My memory is somewhat hazy, but I recall doing this for zonal  
>> means by locally SUMMING the variable in x and putting
>> that sum in a (local) array of length number of local y points.  
>> Then I believe I did an MPI_Gather (or perhaps MPI_Gatherv)
>> to collect those local arrays on root. Then its a simple matter to  
>> computing zonal means from this information. A bit of a hack
>> but it seemed to work.
>>
>> Another possibility (which I haven't tried) would be to create a  
>> new communicator between a group of processors with
>> MPI_Comm_create ( MPI_Comm comm, MPI_Group group, MPI_Comm  
>> *comm_out )
>> and then using the allreduce operation on that comm.
>>
>> Samar
>>
>> On Jan 17, 2008, at 7:57 AM, Martin Losch wrote:
>>
>>> Hi there,
>>>
>>> in a multiprocessor set up I would like to compute a zonal (in i- 
>>> direction) or meridional (in j-direction) mean for an online  
>>> diagnostic. Is there a convenient way of doing this in the MITgcm  
>>> or will I have to get out my MPI handbook (not that I know how to  
>>> use it)?
>>>
>>> In ebm_zonalmean I see an example with global_sum, but I am not  
>>> sure that this will work, as global_sum contains an MPI_Allreduce  
>>> which should (in my view of the world) sum over all processors  
>>> and not only over the zonal ones.
>>>
>>> Martin
>>> _______________________________________________
>>> MITgcm-support mailing list
>>> MITgcm-support at mitgcm.org
>>> http://mitgcm.org/mailman/listinfo/mitgcm-support
>>
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