[Trilinos-Users] creating Tpetra maps from off-processor data

[Siva Rajamanickam]

When one has the "export" list it is not straightforward, but it is not that 
hard. You could use the Distributor's createFromSends() call and do a 
doPostAndWait().

Siva

On 11/05/2014 11:53 AM, Erik Boman wrote:
> In Zoltan terms: if each MPI process has an "import" list of gids, it is easy 
> to use Tpetra to construct a map and do the desired import/export operation, 
> but if each MPI process only has its own "export" list, it's not so simple.
>
> Erik
>
> Templeton, Jeremy Alan wrote:
>> Hi Mark,
>>
>> A simple example of the case we are considering is that process 1 owns a 
>> global id *and* knows that process 0 needs access to that global id’s data.  
>> However, process 0 doesn’t know anything about that global id because it 
>> doesn’t own it.  The current approach is for process 1 to do a specialized 
>> send to process 0, which then uses that information to create a map with 
>> specified global ids to use with importers.
>>
>> The genesis of the question was that it seems like a lot of effort for 
>> something Trilinos might have already as this seemed like a common case, i.e. 
>> having process 1 create a map for process 0.  The documentation for the 
>> constructor you mention has the argument
>>
>> elementList     [in] List of global indices owned by the calling process
>>
>>
>> which implied to us (and we have only ever used as) a list of global indices 
>> the process calling the constructor owns (or at least knows about somehow).  
>> What we would want in this case is for process 1 to assemble that element 
>> list *and* associate it with a target process.  If this sort of functionality 
>> doesn’t exist, no worries, we were just making sure we don’t do a lot of 
>> needless MPI-like coding.
>>
>> Thanks,
>> Jeremy
>>
>> On Nov 5, 2014, at 10:26 AM, Hoemmen, Mark <mhoemme at sandia.gov 
>> <mailto:mhoemme at sandia.gov>> wrote:
>>
>>>
>>>
>>> On 11/4/14, 12:00 PM, "trilinos-users-request at software.sandia.gov 
>>> <mailto:trilinos-users-request at software.sandia.gov>"
>>> <trilinos-users-request at software.sandia.gov 
>>> <mailto:trilinos-users-request at software.sandia.gov>> wrote:
>>>
>>>>
>>>>
>>>> Message: 1
>>>> Date: Tue, 4 Nov 2014 00:47:11 +0000
>>>> From: "Templeton, Jeremy Alan" <jatempl at sandia.gov 
>>>> <mailto:jatempl at sandia.gov>>
>>>> To: "trilinos-users at software.sandia.gov 
>>>> <mailto:trilinos-users at software.sandia.gov>"
>>>> <trilinos-users at software.sandia.gov 
>>>> <mailto:trilinos-users at software.sandia.gov>>
>>>> Subject: [Trilinos-Users] creating Tpetra maps from off-processor data
>>>> Message-ID: <D57C2643-EA3A-40F1-9BE2-AC28DCCA1D9C at sandia.gov 
>>>> <mailto:D57C2643-EA3A-40F1-9BE2-AC28DCCA1D9C at sandia.gov>>
>>>> Content-Type: text/plain; charset="windows-1252"
>>>>
>>>> Hi all,
>>>>
>>>> We are trying to create importers for a particle scheme which which
>>>> communicate on-processor data to neighboring processors.  We have seen
>>>> some codes creating custom Zoltan_Comm_Obj?s to do this task such that
>>>> the processor figures out which particles it needs to send to which other
>>>> processors and executes that through the Zoltan_Comm_Obj. We think we
>>>> can accomplish this same task using the Teuchos comm with
>>>> non-interrupting sends and receives.
>>>>
>>>> However, this seems to be a lot of effort to do something which seems
>>>> like a common and high-level task: create a map from distributed
>>>> information to be used with an importer.  So the question we have is: is
>>>> there functionality within Tpetra/Teuchos which can more directly perform
>>>> this task?
>>>
>>> Hi Jeremy -- could you please clarify what you mean by "create a Map from
>>> distributed information"?  Do you mean that each MPI process knows what
>>> global indices it has, but doesn't necessarily know the other processes'
>>> global indices?  If so, then you could just use the third (noncontiguous)
>>> Map constructor.
>>>
>>> mfh
>>>
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>>
>>
>> --------------------------------------------------------
>> Jeremy A. Templeton, Ph.D.
>> Thermal/Fluid Sciences & Engineering
>> jatempl at sandia.gov <mailto:jatempl at sandia.gov>
>> http://tiny.sandia.gov/jatempl
>> 925-294-1429
>>
>>
>>
>>
>>
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