Diffusion coefficient

[Elizabeth Tseng]

Hi,
    I'm new to both fipy and PDEs. I'm trying to construct a transient 
term that looks like this:

\frac{\partial PHI}{\partial t} = (D / (r^2)) \frac{r^2 \frac{\partial 
PHI}{\partial r}}{\partial r}

I know the left hand term should be a Transient Term. But what about the 
right hand term? The coefficient, instead of being a fixed constant D, 
is D / (r^2)...

Thanks,
Liz