c positive
  definite matrix (R = R**T), and denote G = op(B)*inv(R)*op(B)'.
  Then, the Riccati equation (1) is equivalent to the standard
  discrete-time matrix algebraic Riccati equation

      X = op(A)'*X*op(A) -                                       (4)
                                             -1
          op(A)'*X*op(B)*(R + op(B)'*X*op(B))  *op(B)'*X*op(A) + Q.

  By symmetry, the equation (1) is also equivalent to
                            -1
      X = op(A)'*(I_n + X*G)  *X*op(A) + Q.

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