[SciPy-Dev] Hankel transforms, again

[Tom Grydeland]

On 2014-03-21, at 23:10, Ralf Gommers <ralf.gommers at gmail.com> wrote:

> On 2014-03-21, at 00:05, Ralf Gommers <ralf.gommers at gmail.com> wrote:
> 
>> > Some motivation for why the original Anderson algorithm is still suitable to add to Scipy would be useful.
>> When I have to start _motivating_ my contributions, I think my work is done.

> I'm sorry, but that's a perfectly valid question for any algorithms we add. I spent quite a bit of effort looking at your code and checking the literature. If we're going to have to deprecate these functions again later because they're not accurate enough while there are improved ones around, we do our users a disservice.

As long as the interface is kept, we can simply replace the implementation.  Deprecation isn’t (shouldn’t be) necessary.

> If there's another dev who happens to be an expert to whom it's obvious that this is a good way to add hankel0/1 (Robert?), then fine. Otherwise 
> you're going to have to help me a bit.

I’m not an expert.  My company needed Hankel transforms at some point, and the precision obtained with these routines was sufficient for our purposes.  We needed something which would work satisfactory for inputs (coordinate in the transformed domain) over several orders of magnitude, for which Anderson’s coefficients worked better than Kong’s.

For the analytically known transforms (e.g. those used in the unit test), it is simple enough to plot relative and absolute errors over several decades, and typical values can be documented.

I’m not using these transforms for my current work, so I am not in a position to volunteer significant development effort along the lines of Anderson’s later papers.  I will happily work on the appearance, interfaces, and documentation of the current routines (as demonstrated already), but if they’re not going to be included anyway, I will rather spend my time elsewhere.

Hence this remark:

>> Until this has been decided, I guess there’s no point in addressing your other comments.

> Ralf

Best regards,

Tom Grydeland