to compile CROP 1.33 on macOS 10.12.5 (and prob other versions)

[dougwyu]

first, install necessary background software: gsl and gnu gcc/g++

brew install gcc 
brew install gsl 
git clone https://github.com/tingchenlab/CROP.git
cd CROP

to use the brew gcc (not the macOS gcc, which is clang and doesn't have omp.h support), edit CROP/Makefile so that the first line reads

CPP = g++-7

this sets g++ to be g++7, which is the brew version. (for future gcc versions, edit accordingly)

make # generates a binary called 'CROPLinux'