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<div style=""> Hi, Petsc Team,<br>
<br>
In finite difference computations, we often utilize schemes of five or more points stencil in one direction. To calculate the interior point next to the boundary, we need to assume one point out of the domain by extrapolation (such as a mirror point). As we
are required to include all interior points and boundary points in the system matrix, does Petsc have any feature to handle these mirror points ? In assembling the matrix for a 3D system of multiple variables and equations, besides setting up the boundary
conditions, I think this will cost lots of extra effort to specially manage the points next to the boundary, if Petsc doesn't have any easy way to do this.<br>
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Thank you.<br>
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<br>
Zhisong Li <br>
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