[Paraview] [Catalyst] Setting the MPI Comm in Python

Thu Mar 10 05:37:33 EST 2016

Hi Andy,

I’m using elsA, a CFD package developed by ONERA in France. I was given a few links by the project manager if you want more information about the software:

•             An Overview of the Multi-Purpose elsA Flow Solver (http://www.aerospacelab-journal.org/sites/www.aerospacelab-journal.org/files/AL2-10.pdf)

•             Advanced Aerodynamic Applications with the elsA Software (http://www.aerospacelab-journal.org/sites/www.aerospacelab-journal.org/files/AL2-12.pdf)

•             The Onera elsA CFD software : input from research and feedback from industry - L. Cambier, S. Heib, S. Plot - Mechanics & Industry, 2013

elsA is written in C++ (plus some Fortran routines) but possesses a user interface in Python. I’m using a mechanism in the code that calls a Python script when the internal finish state machine changes state (e.g.: at each increment, before the computation, at the end, …).

Hope that answers your question. Let me know if you want more information ;).

Yohann

From: Andy Bauer [mailto:andy.bauer at kitware.com] 
Sent: Wednesday, March 09, 2016 4:41 PM
To: VAUTRIN Yohann (SAFRAN)
Cc: paraview at paraview.org
Subject: Re: [Paraview] [Catalyst] Setting the MPI Comm in Python

Hi Yohann,

Glad to hear that you were able to get it working! By the way, what simulation code are you instrumenting to use Catalyst if you don't mind saying? I'd be interested to know how it works for you.

Best,

Andy

On Wed, Mar 9, 2016 at 5:34 AM, VAUTRIN Yohann (SAFRAN) <yohann.vautrin at safran.fr> wrote:

Hi Andy,

Thank you for your feedback, it helped me solve my problem.

If anyone is having a similar problem, what I ended up doing is:

import mpi4py.MPI as MPI

import vtk

comm = MPI.COMM_WORLD

rank = comm.Get_rank()

size = comm.Get_size()

in_subcomm = [0,3,6,9] # list of ranks to include in the VTK communicator

subcomm = comm.Split(1 if rank in in_subcomm else 0,rank)

#--- In another part of the program called only by the procs in in_subcomm

vtkComm = vtk.vtkMPI4PyCommunicator.ConvertToVTK(subcomm)

vtkCont = vtk.vtkMPIController()

vtkCont.SetCommunicator(vtkComm)

vtk.vtkMPIController.SetGlobalController(vtkCont)

Due to the way my application works, I had to split the communicator myself, i.e. without using CreateSubController() or PartitionController() because vtk is loaded only by some procs and not every single one (a Mpi_Comm_split operation would therefore be impossible to do).

--

Yohann

From: Andy Bauer [mailto:andy.bauer at kitware.com] 
Sent: Sunday, March 06, 2016 12:55 PM
To: VAUTRIN Yohann (SAFRAN)
Cc: paraview at paraview.org
Subject: Re: [Paraview] [Catalyst] Setting the MPI Comm in Python

Hi,

Can you use a different controller that has the same MPI processes assigned to it? If that works for you, you should be able to just create a vtkMPIController and use either CreateSubController() or PartitionController() to create one similar to what you want. Note that you may need to create two vtkMPIControllers, one that corresponds to MPI_COMM_WORLD and one for your partitioning. After you've done that you can use the vtkMPIController::SetGlobalController() to have VTK and ParaView use that for interprocess communication.

Best,

Andy

On Fri, Feb 26, 2016 at 10:09 AM, VAUTRIN Yohann (SAFRAN) <yohann.vautrin at safran.fr> wrote:

Hi,

I’m working on a Catalyst adaptor written in Python for one of the CFD codes I use at work and I’m having trouble setting the MPI communicator I want the vtkCPProcessor object to use (in order to use a subset of MPI_COMM_WORLD). The MPI communicator I create is a mpi4py.MPI_Comm object, which I convert to a vtkMPICommunicator object using vtk.vtkMPI4PyCommunicator.ConvertToVTK. However vtk.vtkPVCatalystPython.vtkCPProcessor.Initialize is expecting a vtkMPICommunicatorOpaqueComm object and there does not seem to be a way for me to create such an object from the Python interface. Am I missing something here or is something not wrapped correctly or wrong?

For the moment I use mpi4py.MPI.COMM_WORLD to test everything. The following minimal example replicates my problem:

import mpi4py.MPI

import vtk

comm = mpi4py.MPI.COMM_WORLD

coprocessor = vtk.vtkPVCatalystPython.vtkCPProcessor()

coprocessor.Initialize(vtk.vtkMPI4PyCommunicator.ConvertToVTK(comm))

The last line fails with this message:

TypeError: Initialize argument 1: method requires a vtkMPICommunicatorOpaqueComm, a vtkMPICommunicator was provided.

I hope I post on the right mailing list as this could actually be a problem in VTK.

Thank you for your help.

Best,

Yohann V.

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