Created by: portnov
A story: I wanted to write some code that uses cubic spline interpolation similar to "Vector interpolation mk3", and... found out that we have 5 (five!) definitions of cubic_spline method in master. Which are all more or less copy-paste of
# spline function modifed from
# from looptools 4.5.2 done by Bart Crouch(all implementations have this comment).
There is also yet another implementation, in form of two classes (more OOP-style) in geom.py by @ly29 , which is not used anywhere.
So when I started to write some new code, I was faced with an idea of writing 7th implementation... no way. So I couldn't stay from moving the implementation from "interpolation_mk3.py" (which seems to be the last) to geom.py, merging with ly29's code. So in this PR we have LinearSpline and CubicSpline classes, which are used in interpolation_mk3. I did not touch other copies for now.
Theoretically, end-user is not able to see any differences before and after this PR, as this is just a movement of the same code from one module to another.
@zeffii could you please review?