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

[Erik Boman]

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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