[petsc-users] Parallel vector with shared memory in Fortran

[Barry Smith]

> On Jun 5, 2017, at 11:20 AM, Francesco Migliorini <francescomigliorini93 at gmail.com> wrote:
> 
> Dear Stefano, 
> Thank you for your answer. I tried to use VecScatterCreateToAll as you suggested but it does not work since the first processor can only view its part of the vector. Here's how I managed the code:
> 
> Vec    fePS
> VecScatter    Scatter
> (...)
> call VecScatterCreateToAll(feP,Scatter,fePS,perr)
> call VecScatterBegin(Scatter,feP,fePS,INSERT_VALUES,SCATTER_FORWARD,perr)
> call VecScatterEnd(Scatter,feP,fePS,INSERT_VALUES,SCATTER_FORWARD,perr)
> call VecScatterDestroy(Scatter,perr)     
> call VecDestroy(fePS,perr)
> 
> As I said, after this piece of code, if I print all the entries of feP

   The vector feP which is parallel remains the same in these calls

> from one processor, the values are correct if they belong to the part of the processor randon values. 

   The vector fePS contains all the values from all the processes on each process after this call.

  Barry

> 
> Bests, 
> Francesco
> 
> 2017-06-05 16:44 GMT+02:00 Stefano Zampini <stefano.zampini at gmail.com>:
> Sorry, bad copy and paste
> 
> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Vec/VecScatterCreateToAll.html
> 
> Il 05 Giu 2017 4:43 PM, "Stefano Zampini" <stefano.zampini at gmail.com> ha scritto:
> petsc-current/docs/manualpages/Vec/VecScatterCreateToAll.html
> 
> Il 05 Giu 2017 4:12 PM, "Francesco Migliorini" <francescomigliorini93 at gmail.com> ha scritto:
> Hello there!
> 
> I am working with an MPI code in which I should create a petsc vector such that all the processes can access to all its entries. So, I tried with VecCreateShared but it does not work with my machine. Then I tried VecCreateMPI but it seems to me that it does not change anything from the usual VecCreate. Finally I found the scatter commands but the examples are a bit tricky. So, are there any other way? If no, could someone please show me how to use scatter in this simple code?
> 
> Vec  feP    !The vector to be shared with all the processes
> (...)
> mpi_np = 2    !The number of processes
> ind(1) = 10   !The global dimension of the vector
> call VecCreate(PETSC_COMM_WORLD,feP,perr)
> call VecSetSizes(feP,PETSC_DECIDE,ind,perr)
> call VecSetFromOptions(feP,perr)
> (...)    !Here feP is filled in
> call VecAssemblyBegin(feP,perr)
> call VecAssemblyEnd(feP,perr)
> 
> Many thanks,
> Francesco
>