spherical diffusion PDE problem

I am attempting to solve this relationship in MATLAB but I'm not quite sure how to convert this into something that MATLAB's pdepe function can solve. This is a spherical system so m=2. I can fill in my boundary conditions accordingly for bcfun and icfun.

Can anyone help please? Would greatly appreciate it. Thanks

[Torsten]

If you set m=2, MATLAB's "pdepe" solves the above equation. But why (-D) instead of D ? Do you want to use a negative value for D ?

[Juliana]

that was a mistake, confused fick's first and second law. youre right -- should be positive D.

so are you saying that this is the default when I put m=2?

i thought i would have to write this out in a different way for matlab to understand. in that case, does g=1? and f=D*DcDx?

thank you very much for the help Torsten.

[Torsten]

See the answer to your second post.