'Evaluates the Ripley K function for the homongeneous Poisson process,
also known as Complete State of Randomness (CSR).
Parameters
radii : 1D array
Set of distances in which Ripley\'s K function will be evaluated.
Returns
output : 1D array
Ripley\'s K function evaluated at ``radii``.'

def poisson(self, radii):

    return ((np.pi * radii) * radii)
