[petsc-users] Modifying an SNES/DM Jacobian

[Richard Katz]

Hi all,

I am solving PDEs on a 1-D domain with a physical length that varies with time as a part of the solution.  By change of variables, the discretised space coordinate is in [0,1].  This introduces a coupling between the time-dependent physical domain size and the PDEs.

I would like to include the domain-size variable as a DOF in my SNES solve, and this can be accommodated as one of the DM-defined DOFs.  However, doing so couples this particular DOF beyond the stencil, to DOFs throughout the domain.  So I would like to modify the auto-generated Jacobian to include non-zeros that capture this coupling (via finite differences).

For the moment, I am not concerned about breaking the parallelism of the code.

Any advice on the approach and PETSc functions that would be best suited would be appreciated.

Thanks,
Richard



___________________________
Richard Foa Katz
Professor of Geodynamics
Dept Earth Sciences, Univ Oxford
https://urldefense.us/v3/__http://foalab.earth.ox.ac.uk__;!!G_uCfscf7eWS!b_oizbw-XnXax6rasRGtsC_i3pUtzbYYkWhRQifVKLUsOk-SsyuNX4kFQfNq7mrf4hiQxhTOt7sa1y3C7LIW-yAqSN0y-aIoV9k$ 

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