def __init__(self, A, b):
self.P = A.T.dot(A)<EOL>self.q = A.T.dot(b)<EOL>self.n = self.q.size<EOL>
Proximal operator for solving a linear least squares system, Ax = b

Parameters
----------
A : array_like
    Sensing matrix (Ax = b)

b : array_like
    Responses (Ax = b)