[petsc-users] Create a nest not aligned by processors

[Berger Clement]

Dear all, 

I want to construct a matrix by blocs, each block having different sizes
and partially stored by multiple processors. If I am not mistaken, the
right way to do so is by using the MATNEST type. However, the following
code 

Call
MatCreateConstantDiagonal(PETSC_COMM_WORLD,PETSC_DECIDE,PETSC_DECIDE,4,4,2.0E0_wp,A,ierr)
Call
MatCreateConstantDiagonal(PETSC_COMM_WORLD,PETSC_DECIDE,PETSC_DECIDE,4,4,1.0E0_wp,B,ierr)
Call
MatCreateNest(PETSC_COMM_WORLD,2,PETSC_NULL_INTEGER,2,PETSC_NULL_INTEGER,(/A,PETSC_NULL_MAT,PETSC_NULL_MAT,B/),C,ierr)


does not generate the same matrix depending on the number of processors.
It seems that it starts by everything owned by the first proc for A and
B, then goes on to the second proc and so on (I hope I am being clear). 

Is it possible to change that ? 

Note that I am coding in fortran if that has ay consequence. 

Thank you, 

Sincerely,

-- 
Clément BERGER
ENS de Lyon
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