Major overhaul of ProxImaL

[antonysigma]

Changelogs:

• Use Meson build system to handle all C++ compile/link dependencies;

• Update Halide code to version 8.0;

• Auto-schedule Halide code whenever possible;

• Add C++/Python interfaces to Halide-generated code with automatic C-to-Fortran casting and dimension broadcasting;

• Rewrite proximal.halide.halide.Halide to leverage on Meson build. ~This change cripples the CUDA engines;~

• Optimize scale-offset routines in prox() and update steps in *admm.solve() with Numexpr, so they can leverage on caching and parallel compute on multicore CPU. This change cripples the CUDA engines;

• Rewrite test scripts in the folder proximal/tests to run via Pytest. Test scripts that are work-in-progress are renamed to _test_*.py

• Rewrite the Travis CI script to test solely the following environment: Ubuntu 18.04 + Halide 8.0 + Python 3.6. There are plans to include Ubuntu 20.04 in the CI test;

• Format C++ code with Google-style guide. Config script included as proximal/halide/.clang-format;

• Format Python code with Google-style guide. Config script included as proximal/.style.yapf.

[antonysigma]

This change also solves #41, #44, #48, #30 and #33. Comments are welcome.

[SteveDiamond]

This is incredible! Will comment as much as I can, but I don't really know much about Halide (Felix handled that part). Very happy to merge this (after comments of course).

[SteveDiamond]

Can you comment on "This change cripples the CUDA engines". What functionality are we losing exactly?

[antonysigma]

Can you comment on "This change cripples the CUDA engines". What functionality are we losing exactly?

I meant those pycuda specific device-host data transfer intrinsic in the module proximal.algorithms.pock_chambolle, namely the following lines of code:

• adapter.scalar(1.0) and
• adapter.to_np(Ktb).

Actually I didn't mean to remove the code. I have now reverted most of them back. The only catch is that Travis CI cannot spawn a GPU machine to test the project. Please feel free to review pock_chambolle.py.

[SteveDiamond]

Ok, it looks fine to me. Should I merge this in?

[antonysigma]

@SteveDiamond Yes please. Thank you very much!

In the meantime, I am working on another draft PR to update test_poisson.py and test_mask.py. I will ping you when I am ready.