[petsc-users] setting up DA matrix for 3D periodic domain

[ilyas ilyas]

Hi,

Manual pages for "MatSetValuesStencil" says that,
"For periodic boundary conditions use negative indices for values to the
left (below 0; that are to be obtained by wrapping values from right edge).
 For values to the right of the last entry using that index plus one etc to
obtain values that obtained by wrapping the values from the left edge.
 This does not work for the DA_NONPERIODIC wrap."

According to this explanation, If I would set up a matrix for 3D periodic
domain using DAs with DA_ XYZPERIODIC,
The code segment given below could handle periodicity "without specifying
boundary information within the loop"   ?

                 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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"
.
.
.

 MatStencil    row(4),col(4,7)
 PetscInt        i1,i7
 PetscScalar  val(7)

i1 = 1
i7 = 7
.
.
.

call DACreate3d(...,DA_XYZPERIODIC,DA_STENCIL_STAR, ... )

call DAGetMatrix(...,A,...)

call DAGetCorners(da,xs,ys,zs,xm,ym,zm,ierr)

do k=zs,zs+zm-1
   do j=ys,ys+ym-1
      do i=xs,xs+xm-1


  val(1) = ...
col(MatStencil_i,1) = i
col(MatStencil_j,1) = j
col(MatStencil_k,1) = k-1

  val(2) = ...
col(MatStencil_i,2) = i
col(MatStencil_j,2) = j-1
col(MatStencil_k,2) = k

  val(3) = ...
col(MatStencil_i,3) = i-1
col(MatStencil_j,3) = j
col(MatStencil_k,3) = k

  val(4) = ...
col(MatStencil_i,4) = i
col(MatStencil_j,4) = j
col(MatStencil_k,4) = k

  val(5) = ...
col(MatStencil_i,5) = i+1
col(MatStencil_j,5) = j
col(MatStencil_k,5) = k

  val(6) = ...
col(MatStencil_i,6) = i
col(MatStencil_j,6) = j+1
col(MatStencil_k,6) = k

  val(7) = ...
col(MatStencil_i,7) = i
col(MatStencil_j,7) = j
col(MatStencil_k,7) = k+1

  call MatSetValuesStencil(A,i1,row,i7,col,val,INSERT_VALUES,ierr)

        end do
    end do
end do


call MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY,ierr)
call MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY,ierr)

"

If it is so, how PETSc does it ? By inserting cyclic contributions arising
from periodicity into the correct locations within PETSc DAs matrix , as it
is done serially ?


Thank you,
Ilyas.
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