[petsc-users] Union of sequential vecs

[Barry Smith]

  Ok, so you want the unique list of integers sorted from all the seq vectors on ever MPI rank?

   VecScatterCreateToAll() to get all values on all ranks (make the sequential vectors MPI vectors instead).
    create an integer array long enough to hold all of them
    Use VecGetArray() and a for loop to copy all the values to the integer array,
    Use PetscSortRemoveDupsInt on the integer array

  Now each rank has all the desired values.



> On Dec 9, 2022, at 3:24 PM, Karthikeyan Chockalingam - STFC UKRI <karthikeyan.chockalingam at stfc.ac.uk> wrote:
> 
> That is where I am stuck, I don’t know who to combine them to get Vec = {2,5,7,8,10,11,12}.
> I just want them in an MPI vector.
>  
> I finally plan to call VecScatterCreateToAll so that all processor gets a copy.
>  
> Thank you.
>  
> Kind regards,
> Karthik.
>  
> From: Barry Smith <bsmith at petsc.dev <mailto:bsmith at petsc.dev>>
> Date: Friday, 9 December 2022 at 20:04
> To: Chockalingam, Karthikeyan (STFC,DL,HC) <karthikeyan.chockalingam at stfc.ac.uk <mailto:karthikeyan.chockalingam at stfc.ac.uk>>
> Cc: petsc-users at mcs.anl.gov <mailto:petsc-users at mcs.anl.gov> <petsc-users at mcs.anl.gov <mailto:petsc-users at mcs.anl.gov>>
> Subject: Re: [petsc-users] Union of sequential vecs
> 
>  
>   How are you combining them to get Vec = {2,5,7,8,10,11,12}?
>  
>   Do you want the values to remain on the same MPI rank as before, just in an MPI vector?
>  
>  
> 
> 
> On Dec 9, 2022, at 2:28 PM, Karthikeyan Chockalingam - STFC UKRI via petsc-users <petsc-users at mcs.anl.gov <mailto:petsc-users at mcs.anl.gov>> wrote:
>  
> Hi,
>  
> I want to take the union of a set of sequential vectors, each living in a different processor.
>  
> Say, 
> Vec_Seq1 = {2,5,7}
> Vec_Seq2 = {5,8,10,11}
> Vec_Seq3 = {5,2,12}.
>  
> Finally, get the union of all them Vec = {2,5,7,8,10,11,12}.
>  
> I initially wanted to create a parallel vector and insert the (sequential vector) values but I do not know, to which index to insert the values to. But I do know the total size of Vec (which in this case is 7).
>  
> Any help is much appreciated.
>  
> Kind regards,
> Karthik.
>  
>  
>  
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