[petsc-users] VecAssembly gives segmentation fault with MPI

[Jed Brown]

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Francesco Migliorini <francescomigliorini93 at gmail.com> writes:

> Hi, thank you for your answer!
>
> Yes xxx_loc means local but it is referred to the MPI processes, so each
> process has different xxx_loc values. 

Always use Debug mode PETSc so we can check when you pass inconsistent
information to Vec.  The global size needs to be the same on every
process.

> Indeed, the program arrives to Petsc initialization with already
> multiple processes. Then I thought Petsc was applied to all the
> processes separately and therefore the global dimensions of the system
> were the local ones of the MPI processes. Maybe it does not work in
> this way... However mm is parameter equal for all the processes (in
> particular it is 3) and the processes do not have exactly the same
> number of nodes.
>
> 2017-04-19 13:20 GMT+02:00 Jed Brown <jed at jedbrown.org>:
>
>> Francesco Migliorini <francescomigliorini93 at gmail.com> writes:
>>
>> > Hello!
>> >
>> > I have an MPI code in which a linear system is created and solved with
>> > PETSc. It works in sequential run but when I use multiple cores the
>> > VecAssemblyBegin/End give segmentation fault. Here's a sample of my code:
>> >
>> > call PetscInitialize(PETSC_NULL_CHARACTER,perr)
>> >
>> >       ind(1) = 3*nnod_loc*max_time_deg
>> >       call VecCreate(PETSC_COMM_WORLD,feP,perr)
>> >       call VecSetSizes(feP,PETSC_DECIDE,ind,perr)
>>
>> You set the global size here (does "nnod_loc" mean local? and is it the
>> same size on every process?), but then set values for all of these
>> below.
>>
>> >       call VecSetFromOptions(feP,perr)
>> >
>> >       do in = nnod_loc
>> > do jt = 1,mm
>>
>> What is mm?
>>
>> > ind(1) = 3*((in -1)*max_time_deg + (jt-1))
>> > fval(1) = fe(3*((in -1)*max_time_deg + (jt-1)) +1)
>> > call VecSetValues(feP,1,ind,fval(1),INSERT_VALUES,perr)
>> > ind(1) = 3*((in -1)*max_time_deg + (jt-1)) +1
>> > fval(1) = fe(3*((in -1)*max_time_deg + (jt-1)) +2)
>> > call VecSetValues(feP,1,ind,fval(1),INSERT_VALUES,perr)
>> > ind(1) = 3*((in -1)*max_time_deg + (jt-1)) +2
>> > fval(1) = fe(3*((in -1)*max_time_deg + (jt-1)) +3)
>> > call VecSetValues(feP,1,ind,fval(1),INSERT_VALUES,perr)
>> >  enddo
>> >          enddo
>> >       enddo
>> >       call VecAssemblyBegin(feP,perr)
>> >       call VecAssemblyEnd(feP,perr)
>> >
>> > The vector has 640.000 elements more or less but I am running on a high
>> > performing computer so there shouldn't be memory issues. Does anyone know
>> > where is the problem and how can I fix it?
>> >
>> > Thank you,
>> > Francesco Migliorini
>>
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