[petsc-users] DMDA and ksp(ex46.c & ex22f.F90)

[Maahi Talukder]

Thank you for your reply.

I still have some confusion. So if (i,j) is a point on the structured grid(
Where "i" is the column and "j" is the row), and the information associated
with the (i,j) point on the grid is stored in some (m,n) location of the
matrix A (Where Ax =b), I still don't
understand why both of  row(MatStencil_i,1) and row(MatStencil_j,1) are
necessary? I mean is it something like mapping "i" from grid to its
location in the matrix? Would you please explain that?

Regards,
Maahi

On Mon, Mar 11, 2019 at 4:41 PM Patrick Sanan <patrick.sanan at gmail.com>
wrote:

> There are two different types of rows and columns:
> 1. Rows and columns in a grid
> 2. Rows and columns in a matrix
>
> "i" and "j"  refer to rows and columns in the grid, but "row" and "col"
>  refer to rows and columns in the matrix.
>
>
>
> Am Mo., 11. März 2019 um 21:18 Uhr schrieb Maahi Talukder via petsc-users <
> petsc-users at mcs.anl.gov>:
>
>> Hello all,
>>
>> I am trying to solve Poisson Equation on structured grid using 9-point
>> stencil in 2D. Now to setup my matrix, I came across C structure MatStencil
>> in ex22f.F90
>>
>>
>> ...........................................................................................................
>>
>> call DMDAGetCorners <https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/DMDA/DMDAGetCorners.html#DMDAGetCorners>(da,xs,ys,zs,xm,ym,zm,ierr)
>> 107:       do 10,k=zs,zs+zm-1108:         do 20,j=ys,ys+ym-1109:           do 30,i=xs,xs+xm-1110:           row(MatStencil_i) = i111:           row(MatStencil_j) = j112:           row(MatStencil_k) = k113:           if (i.eq.0 .or. j.eq.0 .or. k.eq.0 .or. i.eq.mx-1 .or. j.eq.my-1 .or. k.eq.mz-1) then114:             v(1) = 2.0*(HxHydHz + HxHzdHy + HyHzdHx)115:             call MatSetValuesStencil <https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatSetValuesStencil.html#MatSetValuesStencil>(jac,i1,row,i1,row,v,INSERT_VALUES <https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/INSERT_VALUES.html#INSERT_VALUES>,ierr)116:           else117:             v(1) = -HxHydHz118:              col(MatStencil_i,1) = i119:              col(MatStencil_j,1) = j120:              col(MatStencil_k,1) = k-1121:             v(2) = -HxHzdHy122:              col(MatStencil_i,2) = i123:              col(MatStencil_j,2) = j-1124:              col(MatStencil_k,2) = k125:             v(3) = -HyHzdHx126:              col(MatStencil_i,3) = i-1127:              col(MatStencil_j,3) = j128:              col(MatStencil_k,3) = k129:             v(4) = 2.0*(HxHydHz + HxHzdHy + HyHzdHx)130:              col(MatStencil_i,4) = i131:              col(MatStencil_j,4) = j132:              col(MatStencil_k,4) = k133:             v(5) = -HyHzdHx134:              col(MatStencil_i,5) = i+1135:              col(MatStencil_j,5) = j136:              col(MatStencil_k,5) = k137:             v(6) = -HxHzdHy138:              col(MatStencil_i,6) = i139:              col(MatStencil_j,6) = j+1140:              col(MatStencil_k,6) = k141:             v(7) = -HxHydHz142:              col(MatStencil_i,7) = i143:              col(MatStencil_j,7) = j144:              col(MatStencil_k,7) = k+1145:       call MatSetValuesStencil <https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatSetValuesStencil.html#MatSetValuesStencil>(jac,i1,row,i7,col,v,INSERT_VALUES <https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/INSERT_VALUES.html#INSERT_VALUES>,ierr)146:           endif
>>
>> .....................................................................................
>>
>> What I am confused about is what it means to have the value of row in i and j directions(row(MatStencil_i,1) & row(MatStencil_j,1)).
>>
>> Same confusion goes for the column values as well. I mean generally in a  2D Matrix row values are in j/y direction and column values are in i/x direction.
>>
>> Could you please explain that?
>>
>>
>> Regards,
>>
>> Maahi Talukder
>>
>> Department of Mechanical Engineering
>>
>> Clarkson University
>>
>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20190311/46553e2e/attachment.html>