> On Sep 4, 2017, at 3:48 PM, zakaryah . <[email protected]> wrote: > > One piece of information that would be useful is what ordering PETSc uses for > the Jacobian in the snes_test_display. Is it a natural ordering, or the > PETSc ordering? For debugging the Jacobian manually, the natural ordering is > much easier to work with.
What is displayed is always the natural ordering (internally it is not the natural ordering). > For -n 1, are the orderings the same? yes > > If I use a MatStencil r to represent a field with 3 degrees of freedom, and > the dimensions of my 3D DMDA are MxNxP, which row of the Jacobian corresponds > to r.i=x, r.j=y, r.k=z, r.c=f? Internally it is complicated but for any viewing it is just the natural ordering and all the degrees of freedom for a single point are next to each other in the vector/matrix.
