MPI question

[Julian]

 Thanks Berend and Matt,

I'm gonna take a look at that book... Luckily, they have an e-book version
through our library!

Julian.

> -----Original Message-----
> From: owner-petsc-users at mcs.anl.gov 
> [mailto:owner-petsc-users at mcs.anl.gov] On Behalf Of Berend van Wachem
> Sent: Monday, October 16, 2006 1:35 AM
> To: petsc-users at mcs.anl.gov
> Subject: Re: MPI question
> 
> Hi Julian,
> 
> I am not affiliated to the petsc-team, but have been using 
> petsc a number of years.
> The idea of MPI is that your whole program get executed on 
> each processor. So getting output twice on each processor is 
> quite normal. So not only PETSC functions are called by each 
> processor, every command you write will be called by each 
> processor. Because variables have different values upon each 
> processor, you can imply slightly different behaviour, or 
> have each processor work on an own data set.
> 
> If you want output, I recommend you to use the PETSC 
> functions for IO: 
> PetscPrintf, or PetscSynchronizedPrintf.
> 
> I found it helpful to read an introduction to MPI, "Using 
> MPI" by Gropp, Lusk, Skjellum.
> 
> Good luck,
> 
> Berend.
> 
> > I am using petsc in my fem program on the supercomputer we 
> have here 
> > at texas a&m univ. I configured petsc to build the 
> libraries with mpi.
> > So, I ran  'mpirun -np 2 /home/j0v1008/bin/alphampi 
> a.alpha' in order 
> > to use
> > 2 processors.
> > Till the point where petsc is initialized, everything looks normal. 
> > From the point petsc in initialized, I get duplicates of everything 
> > that is written to cout (at the very least, maybe it's doing 
> > duplicates of other things as well).
> > I understand that all the petsc functions might be called 
> twice or so 
> > depending on how it parallelizes, but I don't understand why it 
> > executes lines that are outside of the petsc world, that 
> have nothing to do with mpi.
> > 
> > Maybe this would clear things up:
> > 
> > void main()
> > {
> > Cout << "line1"
> > //insert code to initialize mpi
> > Cout << "line2"
> > MyfunctionusingMPI()
> > Cout << "line3"
> > //insert code to finalizeMPI
> > }
> > 
> > Say I run this program with 2 processors, will "line2" be printed 
> > twice ? If yes, can you explain why it does that when I 
> didn't ask for 
> > that line to be parallelized?
> > If no, then why is my fea program behaving so?
> > 
> > Thanks,
> > Julian.
> > 
>