  The explicit analytical expression of the Nonlinear Fourier Transform (NFT)
of a finite set of data is provided. Then a simple recursion relation for the
NFT is constructed as a function of the spectral parameter. These tools provide
a complete characterization of the nonlinear coherent structures (solitons,
breathers, ...) present in numerical or experimental data representing the
solution, at a given value of time, of a nonlinear evolution equation (e.g. of
the nonlinear Schroedinger family).
