itaps-parallel Questions about iMeshP

[Tim Tautges]

I was referring here to an implementation that used iMesh vertices as the data structure to represent particles, thus 
the partition of particles would look like partitioning a group of iMesh vertices.  I think your answers imply that a 
second element partition is done accounting for particle weights.  Which raises the question: can a given element be in 
multiple partitions (not parts, that is already not allowed)?

- tim

Devine, Karen D wrote:
> Hi, Tim.
> 
> I'm not sure what you mean by "partices with vertices."  But I'll describe
> what I've seen with PIC codes.
> 
> All the PIC codes I've seen up-close use a static graph-based partition of
> the mesh for the finite-element computation.  Then they use a geometric
> partition for the particle calculation.  Some partition the particles
> directly (i.e., give geometric coordinates for the particles).  Others
> weight mesh elements by the number of particles they contain and then apply
> the geometric partitioner to the weighted mesh.  They use a geometric
> partitioner because (1) they partition the particles frequently and need a
> fast partitioner, and (2) the geometric locality of particles is important
> in the particle calculations.
> 
> The same two reasons apply to the contact problem; replace "particles" with
> "surfaces."
> 
> Karen
> 
> 
> On 12/21/09 9:56 AM, "Tim Tautges" <tautges at mcs.anl.gov> wrote:
> 
>> Interesting.  I've thought about PIC codes in the context, but always wondered
>> whether apps would consider it overkill
>> to do the particles with vertices (which I think is what you're implying
>> below?  Or not?)
>>
>> - tim
>>
>> Devine, Karen D wrote:
>>> Thanks, Tim, for providing a good example.  Here's another:  a
>>> particle-in-cell code can partition the mesh one way for force calculations
>>> and a different way for particle calculations.  The force calculations use a
>>> static partitioning; the particle calculations use a dynamic partitioning
>>> that attempts to maintain particle balance.
>>>
>>> Karen
>>>
>>>
>>>
>>>
>>>
>>> On 12/18/09 9:54 AM, "Tim Tautges" <tautges at mcs.anl.gov> wrote:
>>>
>>>> The best example, brought up by both Karen and me IIRC, is of
>>>> large-deformation transient dynamics with contact, where
>>>> the FE solution of the dynamics is solved on 3d elements on one partition,
>>>> and
>>>> the contact solution is solved on faces
>>>> on a different partition.  Many believe it was this capability that made
>>>> truly
>>>> scalable parallel FEM with contact even
>>>> possible.  See e.g.
>>>>
>>>> Transient dynamics simulations: parallel algorithms for contact detection
>>>> and
>>>> smoothed particle hydrodynamics,
>>>> Proceedings of the 1996 ACM/IEEE conference on Supercomputing, 1996.
>>>>
>>>> That's just one reference, there are many others for that particular work.
>>>>
>>>> I think the details of multiple *active* partitions still need some work,
>>>> both
>>>> in use cases and in how they behave under
>>>> iMeshP.  Normally I wouldn't advocate such an unexplored thing being part of
>>>> the initial interface definition, but in
>>>> this case I think it's an important enough capability that it's justified.
>>>>
>>>> - tim
>>>>
>>>> Mark Beall wrote:
>>>>> As a more general context to the questions that Saurabh asked, the main
>>>>> questions we have about iMeshP are issues related to having multiple
>>>>> partitions. Although we won't be supporting that for now (since our
>>>>> software doesn't support that), it would be helpful in understanding
>>>>> that need if someone could give some examples of how this functionality
>>>>> would be used.
>>>>>
>>>>> mark
>>>>>
>>>>>
>>>> --
>>>> ================================================================
>>>> "You will keep in perfect peace him whose mind is
>>>>    steadfast, because he trusts in you."               Isaiah 26:3
>>>>
>>>>               Tim Tautges            Argonne National Laboratory
>>>>           (tautges at mcs.anl.gov)      (telecommuting from UW-Madison)
>>>>           phone: (608) 263-8485      1500 Engineering Dr.
>>>>             fax: (608) 263-4499      Madison, WI 53706
>>>>
>>>>
>>>>
>>>
>>>
>> --
>> ================================================================
>> "You will keep in perfect peace him whose mind is
>>    steadfast, because he trusts in you."               Isaiah 26:3
>>
>>               Tim Tautges            Argonne National Laboratory
>>           (tautges at mcs.anl.gov)      (telecommuting from UW-Madison)
>>           phone: (608) 263-8485      1500 Engineering Dr.
>>             fax: (608) 263-4499      Madison, WI 53706
>>
>>
>>
> 
> 
> 

-- 
================================================================
"You will keep in perfect peace him whose mind is
   steadfast, because he trusts in you."               Isaiah 26:3

              Tim Tautges            Argonne National Laboratory
          (tautges at mcs.anl.gov)      (telecommuting from UW-Madison)
          phone: (608) 263-8485      1500 Engineering Dr.
            fax: (608) 263-4499      Madison, WI 53706