Functor for the HANKEL projector.
>>> from numpy.random import rand, seed
>>> import numpy as np
>>> M = np.round(
rand(5,5), decimals=2)
>>> M
array([[0.37, 0.95, 0.73, 0.6 , 0.16],
[0.16, 0.06, 0.87, 0.6 , 0.71],
[0.02, 0.97, 0.83, 0.21, 0.18],
[0.18, 0.3 , 0.52, 0.43, 0.29],
[0.61, 0.14, 0.29, 0.37, 0.46]])
>>> p = hankel(M.shape)
>>> p(M)
array([[0.1613085 , 0.24196275, 0.11771161, 0.28555964, 0.21798446],
[0.24196275, 0.11771161, 0.28555964, 0.21798446, 0.17220772],
[0.11771161, 0.28555964, 0.21798446, 0.17220772, 0.13079068],
[0.28555964, 0.21798446, 0.17220772, 0.13079068, 0.14386974],
[0.21798446, 0.17220772, 0.13079068, 0.14386974, 0.2005457 ]])