On Sep 19, 2008, at 10:40 AM, Zhiwen Liang wrote:
It seems that the "var.getFaceGrad()" gives better resolution of the
field stored in "var" than the "var.getGrad()". This is why I was
trying to use FaceVariable in one of the equation terms.
That depends on what you mean by "better resolution". If anything, I
would expect `getGrad()` to be smoother, which is generally better.
The problem I am solving needs a very fine mesh. So I thought it
might be improved if I use the face variable.
I think there's a conceptual error here. If you need a fine mesh, then
make a fine mesh. The FaceVariables are not any finer than the
CellVariables; they're just displaced by half a grid-spacing. By
definition, FiPy solves equations at Cell centers (CellVariables).
Fluxes occur between Cells (diffusion & convection) and call for
coefficients that are FaceVariables. Sources (transients and sources)
change the value at Cells and therefore *must* be defined using
CellVariables.
There are any number of reasons why you might be getting poor results.
Under-resolution is an obvious one: refine your mesh.
Conceivably, `getGrad()` is an inadequate discretization for your
needs, in which case we can look into coding up a higher-order
discretization.
Quite possibly, the issue is elsewhere altogether, though. What is the
physical process you are trying to model? What behavior are you seeing
that leads you to believe that you have a problem?
