Hi,(adsbygoogle = window.adsbygoogle || []).push({});

I seem to have forgotten some of my math how-to, as I havent done this in a while. Looking through my notes, Bird, Stewart and Lightfoot, Greenberg, etc. dont really help.

My equation is this, at steady state:

0 = 1/r^2 ∂/∂r (D*r^2 ∂C/∂r) + P

Where P is some production rate.

So the thing that I'm just not remembering is how to deal with the basic function:

∂/∂r (r^2 ∂C/∂r) in terms of how to deal with it to make it solvable.

I was kind of under the impression that I should do a chain rule to make it a real ODE, which gives me:

0 = D*( ∂2C/∂r2 + 2/r ∂C/∂r) + P

Problem is that the 2/r would integrate into log(r). Implementing the BC for the sphere that at r=0, ∂C/∂r=0, I would have an undefined answer since I'd have Log(0).

So something is wrong.

Ive tried searching around, but most places just glaze over the operation to solve this. I dont think it is that hard, but my brain is empty on this at this point - Ive forgotten how.

Can anyone advise and/or point me in the right direction?

Thanks very much!

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Forgotten my maths! Simple 1D ODE, spherical coordinates

**Physics Forums | Science Articles, Homework Help, Discussion**