Installation issues

[pmli]

I found a few issues with the installation instructions in README.md:

1. It seems that the minimal required Python version is 3.5 (the @ operator is used in linear_model/_linear_model.py).
2. Running pip install pynumdiff in a fresh virtual environment brings up issues with pychebfun for me. It seems that numpy, scipy, and matplotlib need to be installed prior to installing pychebfun (and pynumdiff).
3. Regarding installing from source, I heard somewhere that pip install . is recommended over python setup.py install. And, indeed, running the latter raises SetuptoolsDeprecationWarning and EasyInstallDeprecationWarning for me.

(This is related to my JOSS review: openjournals/joss-reviews#4078)

[florisvb]

Thanks for identifying these issues. I have attempted to resolve all of them through various methods.

1. I removed the @ operator (replaced with cvxpy.matmul), though I also added python>=3.5 as a requirement, though in principle most of the code should work on python 2.7.
2. I removed pychebfun and cvxpy as requirements, and added them as optional requirements. This eliminates that particular issue, furthermore, pychebfun is only required for one option, and there is no need to require all users to have this installed.
3. It is challenging to meet all the installation requirements (especially on an older system like Ubuntu 16.04). To help with this I added more detailed install instructions include several examples that work through a complete install in an empty virtual environment.

Let me know if these changes resolve the issues raised.

[pmli]

Ok, thanks, I guess this resolves the issues, so I'll close this. I would just add some comments:

1. From using vermin, it seems that the minimum required Python version is 3.3. (I do not mean to suggest with this that PyNumDiff should support Python versions that had reached their end of life.)
2. Sounds good.
3. When I had been using Ubuntu 16.04, I had a good experience using pyenv to install newer versions of Python without admin privileges. Does this help you to avoid the installation instructions for these cases?