Move from corr2 to corr2 v3.0 aka TreeCorr

[msimet]

As many of you know, we rely right now on the program corr2 written by Mike Jarvis (@rmjarvis) to do all of our correlation functions. corr2 is a compiled program, and we have been writing catalogs to disk and calling the program via the subprocess module in order to use it.

Today, a new version (v3.0) was released, including a Python interface called treecorr. It's a GitHub repository: https://github.com/rmjarvis/TreeCorr. I propose that we move to this version of the code rather than the old compiled v2.x. It has a number of benefits:

• It will use the catalogs we already have in memory.
  • No need to write catalogs to disk and then read them back in.
  • No further need for a large chunk of code I was never very comfortable with (the function that coerces all the catalogs to the same format and writes them out). As a side benefit, not needing this function renders bug #23 obsolete, and also makes issue #28 easier, among others.
  • No need to make users writing their own data interfaces to figure out when it's easier to send a filename and when it's easier to send an array. We'll just always use arrays.
• Native Python wrappers mean we can remove some of the code in corr2_utils.py and rely on the package's own built-in functions, so we won't be as vulnerable to minor changes in the package.
• Installation is easier than corr2 installation (which was already very simple). You can pip install TreeCorr or clone/download the repo and use the provided installation script. CFITSIO is no longer required.

Mike was kind enough to let me investigate this version before it was released, so shortly I'll be pushing a branch that has some working code on it, although it's not flexible enough yet (has some hardcoded things just so I could check the script functionality).

I suppose I should back up: does anyone have any objections to this change? If so, please do let me know!

[rmjarvis]

Of course if there are any features you need from TreeCorr to make it work better in Stile, please don't hesitate to ask. :)

[rmandelb]

You already know what I think, but for the sake of the others who might not be aware: I fully support this change!

[HironaoMiyatake]

+1 :)

[msimet]

Will do, thanks!