MPI related question: how to evaluate a coefficient function

Guosheng Fu
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5 years 7 months ago #1543 by Guosheng Fu

MPI related question: how to evaluate a coefficient function was created by Guosheng Fu

I am trying to evaluate a grid function at a specific mesh point, but it failed for the MPI version with the following snippet...

Code:

if mesh.Contains(0,0): 
    gfu(mesh(0,0))

lkogler
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5 years 7 months ago - 5 years 7 months ago #1548 by lkogler

Replied by lkogler on topic MPI related question: how to evaluate a coefficient function

It looks like empty meshes (rank 0 has no elements) are not handled correctly.
As a workaround:

Code:

if mesh.comm.rank!=0 and mesh.Contains(0,0):
    gfu(mesh(0,0))

Should be fixed shortly.

Last edit: 5 years 7 months ago by lkogler.

Guosheng Fu
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5 years 7 months ago #1549 by Guosheng Fu

Replied by Guosheng Fu on topic MPI related question: how to evaluate a coefficient function

Thanks!
Say, do you have any suggestions on code debugging in MPI?
It would be a good exercise for me to trace a bug and try to fix it myself first before asking these small questions...

lkogler
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5 years 7 months ago - 5 years 7 months ago #1553 by lkogler

Replied by lkogler on topic MPI related question: how to evaluate a coefficient function

I have not found a solution I am really satisfied with myself, but I can tell you what I usually do.
Just keep in mind that this is all just cobbled together.

For small jobs, you can run each MPI process in a seperate xterm-window and attach gdb to each of them.

Code:

mpirun -np 1 gdb -ex run --args python3 PYTHON_SCRIPT : \
             -np X xterm -hold -e gdb -ex run --args  python3 PYTHON_SCRIPT

You can also pipe the output of each process to a seperate file, for example, with OpenMPI you could write
a small script like this:

Code:

#!/bin/sh
$@ 1>out_p$OMPI_COMM_WORLD_RANK 2>err_p$OMPI_COMM_WORLD_RANK

Then you can use gdb on each process, and tell it to print the back-trace when it encounters a problem

Code:

mpirun -np X  bash WRAP_SCRIPT gdb -batch -ex "run" -ex bt --args python3 PYTHON_SCRIPT 

This way you can do bigger jobs, but you cannot use gdb interactively.

This also works with valgrind instead of gdb.

Last edit: 5 years 7 months ago by lkogler.

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