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NuFast is designed to calculate all nine neutrino oscillation probabilities in matter for long-baseline accelerator (e.g. NOvA, T2K, DUNE, HK) and reactor experiments (e.g. JUNO) very quickly, using the algorithms optimized for realistic oscillation scenarios. NuFast is provided in fortran, c++, and python, although no particular guarantees are made that the python code is "fast".
The folders for each language contain a minimal working implementation to calculate the probabilities in matter and vacuum. The functions take as input the six oscillation parameters, with the mixing angles in the form of s12sq and so on. The CP violating phase, delta, is in radians. The atmospheric mass ordering is set by the sign of Dmsq31. The mass-squared differences are in eV2. For antineutrinos change only the energy to negative. The neutrino energy is in GeV, the baseline is in km, and the density is in g/cc. The electron fraction, Ye, is typically about 0.5 in the Earth. The function returns a 3x3 array probs_returned which contains all nine channels. The first index corresponds to the initial neutrino flavor (fortran is 1-indexed so e=1, while c++ and python are 0-indexed so e=0). Finally, the N_Newton parameter provides a proxy for the precision. N_Newton=0 is already precise enough for even the next generation of neutrino oscillation experiments and higher values add orders of magnitude to the precision for minimal computational cost.
The code can be compiled with the simple compile.sh file provided in the fortran and c++ folders. The benchmark codes can be compiled with the given makefiles by running make. The inclusion of aggressive compiler flags like -ffast-math can be included or not.
If a user requires a python code, we recommend the use of cython, f2py, or something similar from the c++ or fortran codes. The python code is included so that those who are only familiar with python can easily parse the algorithm itself, not for efficient computations.
The benchmark folder contains the same code in a slightly different structure, as well as some other neutrino oscillation probability codes. It computes the precision of the NuFast algorithm and also benchmarks the computational speed.
The included GLoBES code is adapted from the well known GLoBES code at https://www.mpi-hd.mpg.de/personalhomes/globes/index.html. If that portion of the code is used, please cite them as appropriate.
Running the GLoBES code requires GSL. The makefile should work fine if it is installed in a typical Linux system.
If you use this code, please cite the associated paper arXiv:2405.02400 by Peter Denton and Stephen Parke. Please also let us know if you find any bugs or further optimizations or if you run your own speed tests.