FPUT Chain Correlation

This release is useful to numericaly compute correlations functions for the periodic FPUT short range chain, i.e. Hamiltonian system with the following Hamiltonian
H = \sum_{j=0}^{N-1} (p_j^2/2 + \sum_{s=1}^m k_s((q_{j+s} - q_j)^2/2 + chi*(q_{j+s} - q_j)^3/3 + gamma*(q_{j+s} - q_j)^4/4) ))
where N is the number of particles, m in fixed and k_s are positive real numbers that can be interpreted as springs constants

There is also a python script that produce the correlation function for the harmonic analogues of the previous chain, i.e. the harmonic chain with short range interaction:
H = \sum_{j=0}^{N-1} (p_j^2/2 + \sum_{s=1}^m k_s((q_{j+s} - q_j)^2/2)