Discussion Forum

I've attached an example .mph file that shows one way (among other possibilities) to solve your problem. It's also rather nice to see it yields the correct answer. :)

Thank you Robert. This works excellently. I guess the mistake I was making was that I was trying to define the derivative by substituting α=-1, instead of β=1.

However, I do have a couple of questions which I would appreciate, if you could find the time to answer.

1. Why does substituting α=-1 (instead of β=1) in the coefficient form PDE not work? If u is a regular valued function, div(u)=du/dx in 1D right?

2. Why does putting a zero flux condition at x=1 not cause an error, or produce incorrect results.

Thanks in advance, AR

Let's talk about your seond item first: The (default) zero flux condition (if you look at the equation for it) involves a relationship among linear operations on c, alpha, and gamma. But all of those coefficients are zero, in the example that I posted, so in that case, the "zero flux" condition doesn't impose any constraint.

Now, regarding your first item, if I were to instead set alpha = -1, then I could no longer ignore that default flux boundary condition (per the comment above). There is probably a way to make that still work (since a variety of other boundary conditions are available), but in my approach, that issue simply never arises. I chose what seemed to me to be the simplest approach.

Thanks Robert. Addresses my queries.

Regards, AR