Dear all, I am new to FreeFEM and have met some problems about MPI recently. My algorithm is an iterative one, and in each iteration, there are many sub-problems that are independent with each other, hence I want to solve them in parallel. However, it seems that every step of the whole algorithm …

Thank you so much for your reply. I will try it.

Thanks for your reply before. I still have some problems on this topic. My code is of this form: Stage 1: not in parallel Stage 2: in parallel Stage 3: not in parallel In addition, Stage2 and Stage3 should be included in iterations. Would you please tell me whether I can just parallelize Stage2 …

You could simply surround stage 1 and stage 3 with if(mpirank == 0) { // do stage 1 or 3 }, but that is extremely wasteful since all other processes will idle. Why are stage 1 and stage 3 not parallel?

Thanks for your reply. Stage 1 produces one solution, which will be used in stage 2. And stage 2 consists of many independent sub-problems, hence it can be parallelized. And stage 3 employs all the solutions of stage 2.

Stage 1 produces one solution Why can’t this be done in parallel? Stage 3 employs all the solutions of stage 2 Again, what makes this stage not runnable in parallel?

Sorry. It definitely could be runnable in parallel and could derive the right solution in all processors. I am a begginer of MPI and I am just wondering whether we can parallelize only part of the code.

I see. It’s actually very easy to parallelize the solution phase using PETSc, you just need to add a couple of keywords. But if you just want to parallelize part of the script, you need to use if conditions with mpirank, as I wrote earlier. But again, that is a rather bad idea, best to use three dif…

That is a nice idea. Thank you so much for your help and patience.

Enquiry about MPI

General Discussion

prj May 28, 2021, 8:56am 2

Please look at this very similar post: Solving a lot of independent ODEs in parallel.

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Enquiry about MPI

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