Matt, Yes I would actually use a[] in this case. Back then, I think I was trying to take the derivative of the auxiliary which i had declared to be piece-wise constant.
The auxiliary a[] is the gradient of pressure (times permeability over viscosity) obtained from solving the Darcy equation as a Laplacian. This part is solved separately, projected as cell-wise velocity, and inputted as an auxiliary for the advection-diffusion problem. Speaking of which, have you had a chance to look into DMPlexProjectFieldLocal(...) not projecting dirichlet BC constraints? I realize that the "small example" I gave you wasn't small at all, so I can send you a smaller and simpler one if needed. Thanks, Justin On Tue, May 5, 2015 at 3:34 PM, Matthew Knepley <[email protected]> wrote: > On Sat, Apr 4, 2015 at 11:54 AM, Justin Chang <[email protected]> wrote: > >> Hi everyone, >> >> I want to include advection into my diffusion FEM code (I am assuming a >> small Peclet number so stability isn't an issue ATM). That is I want to >> incorporate the second term as a pointwise function: >> >> du/dt + v * grad[c] - div[grad[c]] = f >> >> Where v is the velocity (obtained from the auxiliary term a_x[]). For the >> residual, would it be of the following form: >> > > 1) I would think you would use a[] instead. What is your velocity the > gradient of? > > >> f0_u(const PetscScalar u[], const PetscScalar u_t[], const PetscScalar >> u_x[], const PetscScalar a[], const PetscScalar a_t[], const PetscScalar >> a_x[], const PetscReal x[], PetscScalar f0[]) { >> >> PetscInt d; >> f[0] = u_t[0]; >> for (d = 0; d < spatialDim; ++d) f0[0] += a_x[d]*u_x[d]; >> >> } >> >> What about the jacobian? My guess would be to use g1(...) but what would >> the inside of this function be? >> > > Yes it would be g1. The indices for the output are f,g,dg. I am guessing > that c is a scalar, so f = {0}, g = {0}, dg = {0, 1} > for 2D, so g1 would have two terms, > > g1[0] = a[0]; > g1[1] = a[1]; > > Thanks, > > Matt > > >> Thanks, >> >> >> -- >> Justin Chang >> PhD Candidate, Civil Engineering - Computational Sciences >> University of Houston, Department of Civil and Environmental Engineering >> Houston, TX 77004 >> (512) 963-3262 >> > > > > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to which their > experiments lead. > -- Norbert Wiener >
