[SciPy-Dev] RBF epsilon (changes 0.15 => 0.16)

[Ariel Rokem]

Hi everyone,

In our work on dipy, we've run into a small issue moving from 0.15 to 0.16:

https://github.com/nipy/dipy/issues/688

The gist of this is that we are using RBF to interpolate a signal measured
on the unit sphere. To do this, we have designed a custom 'norm' function
based on the angle between measurements (rather than the default
Euclidean). Code is here:

https://github.com/nipy/dipy/blob/master/dipy/core/sphere.py#L500

This seemed to work fine with 0.15, but the changes to the default epsilon
introduced here: https://github.com/scipy/scipy/pull/4643 seem to be
throwing us off.

I've taken a look at the discussion on that PR and the issue that led to
this work, and it does make sense, but I wanted to get some feedback to see
how we should proceed. Setting a larger default epsilon in our code
(effectively undoing this change) would be one way to go, but I want to
make sure that it wouldn't be an obvious blunder, and that there isn't some
issue on scipy that we should be thinking about.

Thanks!

Ariel
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