Use of acor package runs into trouble with more recent Numpy versions

[Hazboun6]

The acor package is no longer under active development and has seen recent issues (@svigeland @kdolum) with newer versions of Numpy. Currently the import used in PTMCMCSampler is inside a try except loop, owing to some of these issues.

There is a nice autocorrelation function inside of emcee and this has recently been used in enterprise_extensions as a replacement for acor.

[Hazboun6]

It is an open question whether we should require either package as requirement for the sampler, but requiring emcee would be a pretty light addition.

[AaronDJohnson]

@Hazboun6 is the license for emcee such that we can just hijack the autocorrelation calculation file and not have any extra requirements (with the proper credits given in the file)?

[paulray]

The docs should also note that acor should not be installed with pip install acor since the PyPI version is different than the current master. It must be installed with pip install git+https://github.com/dfm/acor.git to get the version that PTMCMCSampler wants.

[kdolum]

The docs should also note that acor should not be installed with pip install acor since the PyPI version is different than the current master. It must be installed with pip install git+https://github.com/dfm/acor.git to get the version that PTMCMCSampler wants.

This is a rather unpleasant situation, exacerbated by the fact that the two different versions of acor have the same version number. If would be nice to avoid this problem by not using it all.