Matthew Knepley <[email protected]> writes: > If you want symmetry, you can do MatZeroRowColumns(). I said is generally > not a good idea because it is more complicated to eliminate > them in the FD case.
I don't agree. > You can definitely do what you propose. With FEM, it makes more sense. You > eliminate constrained variables from the system, but > keep the values in the local vector. Then when you do an element integral, > you get the correct answer including the boundary > conditions, and everything is natural. Assuming you are working with a nonlinear problem in defect correction form (e.g., Newton). This simple procedure works fine for FD and FE, to evaluate the residual F(U) and the "Jacobian" or Picard matrix J(U): Scatter UGlobal to ULocal Write correct Dirichlet values into ULocal Evaluate local residual FLocal(ULocal) and scatter to global if applicable Set Dirichlet nodes of FGlobal to UGlobal - UDesired Assemble J at ULocal, ignoring Dirichlet rows and columns Insert 1 on diagonal of Dirichlet rows and columns
pgpMzvuELPK9J.pgp
Description: PGP signature
