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Dear Nektar++ developers,

I am currently trying to run a CWIPI–Nektar++ coupled example on Archer2, where a Python program (CWIPI source side) sends data to Nektar++ (AcousticSolver) to compute APE. I would like to confirm whether my setup steps are correct and ask for any advice from those who have successfully used CWIPI with Nektar++.

1. CWIPI side (Python)

CWIPI initialization is done as follows:

comm = MPI.COMM_WORLD

code_name = "PyApp"

coupled_code_name = "NekApp"

intra = pycwp.init(comm, [code_name], True)

cpl = pycwp.Coupling(

code_name,

"LambFile", # matches XML coupling name

coupled_code_name,

2. Nektar++ side

In the Nektar++ XML condition file (Condition_try.xml), the coupling section is:

# the variables for source are set to 0 in source function

</COUPLING>

Nektar++ is started with: AcousticSolver --cwipi 'NekApp' mesh.xml Condition.xml --verbose

so the local code name is "NekApp", matching the coupled_code_name in the Python script.

3. Archer2 run setup

I created two shell scripts:

run_cwipi.sh:

export MPICH_SMP_SINGLE_COPY_MODE=CMA

source ...

exec python -u cwipi_source.py

run_nek.sh (Nektar++ side):
export ...

exec AcousticSolver --cwipi 'NekApp' mesh.xml Condition.xml --verbose

and a .conf file--multi.conf:

0 ./run_cwipi.sh

1 ./run_nek.sh

Run command on Archer2:

srun --ntasks=2 --multi-prog multi.conf

4. The issue
When running, both sides print the CWIPI initialization banner:

cwipi 1.3.0 initializing

------------------------

5. Request for advice

I would like to confirm:

Is my CWIPI–Nektar++ code-name mapping correct (PyApp ↔ NekApp, "LambFile" coupling name)?

Is srun --multi-prog with shared MPI_COMM_WORLD the recommended way for intra-communicator mode?

Are there known restrictions in CWIPI–Nektar++ coupling when each code only has one MPI rank?

Could there be additional configuration required on the Nektar++ side for CWIPI to complete initialization?

Any guidance or examples from someone who has successfully run CWIPI with Nektar++ would be very helpful.

Thank you in advance for your time and assistance.

Best regards,

Dao