Re: Diffusion equation with a moving point source

On Jun 23, 2008, at 2:19 PM, Jonathan Guyer wrote:
> I would do it like this:
>
> xVar = CellVariable(mesh=mesh, value=x)
> delta = 1. * ((xVar > x_s) & (xVar < x_s + 1))

Thanks. This is exactly what I was trying to do.

>> But I believe this gives me an incorrect solution (checked against  
>> analytical solution) since the time integration would assume that  
>> the source has a fixed position during each time interval `dt`.
>
> The time integration is first order and the way I declare delta  
> above should have the exact same effect as moving delta.setValue  
> into the loop.

Hmm, that makes sense. Somehow I think I should have realized that  
these were the same.

> Do you get better agreement if you reduce the timestep?

Yeah, smaller timesteps help;  the convergence is a little slower than  
I imagined, though. I may have some other errors in my code that's  
causing problems (my actual code isn't the same as the example I gave).

Thanks for your help!
-Tony