[petsc-users] Partition of parallel AIJ sparce matrix

[Qin Lu]

In the context of domain decompostion, if the unknowns are ordered (to reduce the number of infills, for instance) in the way that each subdomain may not own consecutive unknown index, does this mean the partition of the domain will be different from the partition of the matrix? 
 
For example, if subdomain 1 (assigned to process 1) owns unknowns 1 and 3 (associated with equation 1 and 3), subdomain 2 (assigned to process 2) owns unknowns 2 and 4 (associated with equation 2 and 4) , how can I make each process own consecutive rows?
 
Thanks,
Qin
 
 From: Barry Smith <bsmith at mcs.anl.gov>
To: Qin Lu <lu_qin_2000 at yahoo.com> 
Cc: petsc-users <petsc-users at mcs.anl.gov> 
Sent: Wednesday, July 30, 2014 2:49 PM
Subject: Re: [petsc-users] Partition of parallel AIJ sparce matrix
  


On Jul 30, 2014, at 11:08 AM, Qin Lu <lu_qin_2000 at yahoo.com> wrote:

> Hello,
>  
> Does a process have to own consecutive rows of the matrix? For example, suppose the global AIJ is 4x4, partitioned by 2 processes. Does process 1 have to own rows 1 and 2, process 2 own rows 3 and 4?

   Yes

> Or process1 may own rows 1 and 3, and process 2 own row 2 and 4?

  However, the numbering of degrees of freedom is arbitrary. Just renumber you degrees of freedom so the first set is on process 0, the next on process 1 etc.

   Barry


>  
> Thanks a lot for your help!
>  
> Regards,
> Qin 
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