James -

I don't think there's a straightforward way to get at this.

You can certainly write the explicit forms, e.g.,

  (DiffCoeff * Psi.faceGrad).divergence

or

  (Psi * convCoeff).divergence

but this isn't exactly the same as the matrix FiPy builds, as discussed at 
https://github.com/usnistgov/fipy/issues/461. 

I can see the value for diagnosing and simply understanding mechanisms, so I'll 
think about ways we might provide access to this.

- Jon

On Feb 12, 2016, at 10:18 AM, James Pringle <[email protected]> wrote:

> I feel this should be an elementary question, but I can't seem to figure out 
> how to answer it. I am solving a simple linear elleptic-ish equation with
> 
> eq = 
> (DiffusionTerm(var=Psi,coeff=DiffCoeff)+ExponentialConvectionTerm(var=Psi,coeff=convCoeff))
> eq.solve(var=Psi)
> 
> This works fine; the solution matches what I would expect.  I have two 
> questions: 
> 
> First, how can I obtain the value of the individual terms of the equation, 
> evaluated with the solution in Psi?
> 
> Second, is there any way to define my own new Psi (which is not an exact 
> solution to the equation), and easily evaluate the DiffusionTerm and 
> ExponentialConvectionTerm for that Psi?
> 
> I am trying to illustrate how various parts of the solution evolve over the 
> solution space, and how various approximations to the full solution differ 
> from the full solution. 
> 
> Thanks to all who glance at this
> James Pringle
> University of New Hampshire
> 
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