Documented _OPENMP preprocessor flag in readme

[tgorni]

When compiled for CPU only, TurboRVB detects automatically whether openmp is supported or not. However, the number of threads is always reported to be one in the output file, since the preprocessor flag _OPENMP is never enabled. The user is now warned of this behaviour in the README.

[kousuke-nakano]

Thank you @tgorni !!

[kousuke-nakano]

I do not get why _OPENMP is not enabled via CMake :-( Do you have any clue?

[tgorni]

My guess is that, while !$omp pragmas are simply ignored by the compiler when openmp is not supported and a single-threaded executable is produced, if _OPENMP is permanently enabled the compilation will crash when openmp is not supported because the compiler will not find omp_* functions.

[addman2]

Hi all, I noticed OMP sometimes does not work with CMake. And honestly this is a mistery to me. This is the reason why I wrote backfall make.inc build. When you compile Turbo make it will work. The mistery here is the Makefile does exactly the same thing as CMake to my knowledge, but with CMake sometimes it does not work but with Makefile it does.

Keep in mind, one has to do more tweeking when installing with make.inc, there are some example make.inc files that should work most of the times.

We need to look at this more carefully.

[kousuke-nakano]

Hi, #105 solved this issue :-)