"spherical polar" coordinates ignore left boundary condition

[bessman]

Describe the bug
When using "spherical polar" coordinates, the left boundary condition seems to always be zero flux, regardless of what the user specifies.

To Reproduce
Steps to reproduce the behaviour:

1. Run the 'Creating Models/2-a-pde-model.ipynb' notebook.
2. Change the left boundary condition type and/or value to anything.
3. Rerun notebook.
4. Final result is the same.

Expected behaviour
The left boundary condition should be user-changeable. Alternatively, if zero flux is intentionally enforced on the left boundary in spherical coordinates, the user should be warned of this fact if they request something else.

[valentinsulzer]

Thanks for pointing out - seems to be something do with with the multiplication by r**2 which we should be more careful about

[brosaplanella]

Hi @bessman! I think that for spherical (and cylindrical coordinates) the condition at r=0 should always be a no-flux condition (note that, in reality, this is an artificial boundary that arises due to the parameterization of the domain). What problem are you trying to solve that gives you a BC other than no-flux?

[bessman]

I noticed it while working through some of the example notebooks. Specifically, in "Creating Models/2-a-pde-model.ipynb", the left boundary condition type is given as Dirichlet in the code. This should result in an incorrect result, but does not, because the boundary condition is ignored.

As you say, that's not typically going to be a problem when dealing with spherical particles. I just think the behavior should be clearly documented if it is intentional, to avoid surprising the user.

[rtimms]

thanks @bessman, it looks like this was a typo in the notebook. as discussed, symmetry always gives no flux at r=0 in spherical polars, but it would be good to add a warning if people try to use a different condition

[brosaplanella]

Cool, I will modify the code so it throws an error if a "left" bc is passed that it is not a no-flux condition.

[valentinsulzer]

@all-contributors add @bessman for bugs, examples

[allcontributors]

@tinosulzer

This project's configuration file has malformed JSON: .all-contributorsrc. Error:: Unexpected token ] in JSON at position 895

[valentinsulzer]

@all-contributors add @bessman for bugs, examples

[allcontributors]

@tinosulzer

I've put up a pull request to add @bessman! 🎉

[valentinsulzer]

Good bot