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

[Martin Losch]

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
>
> _______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mitgcm.org/mailman/listinfo/mitgcm-support