compute ML beta

def beta_hat(self):
        """compute ML beta"""
        XKY = self.XKY()
        XanyKY = self.XanyKY()
        beta_hat, beta_hat_any = self.Areml_solver.solve(b_any=XanyKY,b=XKY,check_finite=True)
        return beta_hat, beta_hat_any