[petsc-users] How to use MatSetValuesStencil() with DOF>1

[Lucas Banting]

Hello,

I have a structured grid problem with 5 unknowns per cell: U,V,P,T,F, this is a CFD code but I don't think these details are necessary to answer my question.
I was wondering how exactly I should use MatSetValuesStencil() to fill my matrix.
I have 5 degrees of freedom, so I need to set up to 25 coefficients per grid cell. I don't understand how i,j, and c map to all coefficients.

For a 1 degree of freedom system to fill my 9 point stencil I did:

          values(1)= ASW(II,JJ)
          values(2)= AS (II,JJ)
          values(3)= ASE(II,JJ)
          values(4)= AW (II,JJ)
          values(5)= AP (II,JJ)
          values(6)= AE (II,JJ)
          values(7)= ANW(II,JJ)
          values(8)= AN (II,JJ)
          values(9)= ANE(II,JJ)

          idxm(MatStencil_i,1) = II;idxm(MatStencil_j,1) = JJ

          idxn(MatStencil_i,1) = II-1;idxn(MatStencil_j,1) = JJ-1
          idxn(MatStencil_i,2) = II    ;idxn(MatStencil_j,2) = JJ-1
          idxn(MatStencil_i,3) = II+1;idxn(MatStencil_j,3) = JJ-1
          idxn(MatStencil_i,4) = II-1 ;idxn(MatStencil_j,4) = JJ
          idxn(MatStencil_i,5) = II    ;idxn(MatStencil_j,5) = JJ
          idxn(MatStencil_i,6) = II+1;idxn(MatStencil_j,6) = JJ
          idxn(MatStencil_i,7) = II-1 ;idxn(MatStencil_j,7) = JJ+1
          idxn(MatStencil_i,8) = II     ;idxn(MatStencil_j,8) = JJ+1
          idxn(MatStencil_i,9) = II+1;idxn(MatStencil_j,9) = JJ+1
          call MatSetValuesStencil(A,1,idxm,9,idxn,values,INSERT_VALUES,ierr)

Which seemed to work just fine. For 5 degrees of freedom, instead of just having a single AP coefficient for example, I have an AP matrix:

ap_uu
ap_uv
ap_up
ap_ut
ap_uf
ap_vu
ap_vv
ap_vp
ap_vt
ap_vf
ap_pu
ap_pv
ap_pp
ap_pt
ap_pf
ap_tu
ap_tv
ap_tp
ap_tt
ap_tf
ap_fu
ap_fv
ap_fp
ap_ft
ap_ff

In 1 degree of freedom, i and j corresponded to the solution variable in the grid. For multi degree of freedom, I don't understand how values of i, j, and c could distinguish from an ap_uv and ap_vv coefficent for example, wouldn't they both be at i, j ,c=2?
Is there anyway I can use MatSetValuesStencil() to fill in my 9 point stencil with my 5x5 matrix coefficients? To clarify I have nine 5x5 matrices for each cell which correspond to the 5 unknowns per cell.

Thanks,

Lucas
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