'Given a policy `sigma`, return the T_sigma operator.
Parameters
sigma : array_like(int, ndim=1)
Policy vector, of length n.
Returns
callable
The T_sigma operator.'

def T_sigma(self, sigma):

    (R_sigma, Q_sigma) = self.RQ_sigma(sigma)
    return (lambda v: (R_sigma + (self.beta * Q_sigma.dot(v))))
