MPI file reader is broken(?)
It seems that the mpi reader is not correct, such that with mpirun -np 2 ./Examples/Debug/ChebyshevInterpolationMPIFMM
the last particles of P0 and the first particles of P1 are the same.
Then, it turns into a NaN.
I am not very confident by the way the readers have been designed, so I let someone else solve this (if no one can, I will try to do it later)
once it is done, one should check that mpirun -np 2 ./Examples/Debug/ChebyshevInterpolationMPIFMM
returns the same energy for different number of processes.