[petsc-users] Request for Assistance with Parallel Matrix Solving Using petsc4py in EasyFEA

[Matthieu Noel]

Sorry for my late response.

I found out how to solve the issue. I had to reorder the DOF ordering to 
ensure the matrix system is continuous: 
https://urldefense.us/v3/__https://github.com/matnoel/EasyFEA/blob/dev/EasyFEA/Simulations/Solvers.py*L523-L618__;Iw!!G_uCfscf7eWS!ZRIBid8MQtxlDGuOHlzwyX677gChgXqdcePniPOa8Samn9v3Sv_ru-0neC8JQXK74zKh9uO9IqyyE9LzQGl-haOxRB1bLFY$  


Best regards,
Matthieu Noel

Le 11/03/2026 à 21:56, Barry Smith a écrit :
>
>    Does it compute the “correct” result with one MPI process?
>
>> On Mar 10, 2026, at 4:29 AM, Matthieu Noel <matthieu.noel at inria.fr> 
>> wrote:
>>
>> Dear PETSc users,
>>
>> My name is Matthieu Noel, and I am a research software engineer at INRIA.
>>
>> During my PhD thesis, I developed *EasyFEA*, an open-source finite 
>> element analysis tool documented here: 
>> https://urldefense.us/v3/__https://easyfea.readthedocs.io/en/stable/__;!!G_uCfscf7eWS!ZRIBid8MQtxlDGuOHlzwyX677gChgXqdcePniPOa8Samn9v3Sv_ru-0neC8JQXK74zKh9uO9IqyyE9LzQGl-haOxE6AgvRk$ .
>>
>> I am currently working on *Issue #26* 
>> (https://urldefense.us/v3/__https://github.com/matnoel/EasyFEA/issues/26__;!!G_uCfscf7eWS!ZRIBid8MQtxlDGuOHlzwyX677gChgXqdcePniPOa8Samn9v3Sv_ru-0neC8JQXK74zKh9uO9IqyyE9LzQGl-haOxEX807cA$ ), where I aim to use 
>> *petsc4py* to solve a simple stationary thermal problem in parallel.
>>
>> The main challenge is *constructing and solving the parallel matrix 
>> system* (|Ax = b|).
>>
>>
>>       Current Status:
>>
>>   * *Mesh partitioning* has been successfully performed using *GMSH*.
>>   * EasyFEA provides the *assembled matrix system* (|Ax = b|) with
>>     applied boundary conditions.
>>   * My current implementation using *petsc4py* runs without errors,
>>     but the results obtained are incorrect.
>>
>> <DbhO7xbQSISvapJk.png>
>> I suspect the problem lies in how the *parallel matrix and vectors 
>> are assembled or solved*, particularly in handling *ghost DOFs* and 
>> ensuring proper communication between MPI ranks.
>>
>> I would be extremely grateful for any guidance, resources, or 
>> examples you could share to help me address this issue.
>> My current development branch is available here: 
>> https://urldefense.us/v3/__https://github.com/matnoel/EasyFEA/tree/26_mpi__;!!G_uCfscf7eWS!ZRIBid8MQtxlDGuOHlzwyX677gChgXqdcePniPOa8Samn9v3Sv_ru-0neC8JQXK74zKh9uO9IqyyE9LzQGl-haOxHLPPL0E$ .
>>
>> The PETSc function can be found at this link: 
>> https://urldefense.us/v3/__https://github.com/matnoel/EasyFEA/blob/26_mpi/EasyFEA/Simulations/Solvers.py*L649-L767__;Iw!!G_uCfscf7eWS!ZRIBid8MQtxlDGuOHlzwyX677gChgXqdcePniPOa8Samn9v3Sv_ru-0neC8JQXK74zKh9uO9IqyyE9LzQGl-haOxwl_Zt5w$ 
>>
>> I am currently running the script in the attached files.
>>
>>
>> Thank you in advance for your time and expertise.
>>
>> Best regards,
>> Matthieu Noel
>>
>>
>>
>> <Thermal1.py>
>
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