r R given in a
  factored form, Q = C'C, R = D'D, and with L a zero matrix.

  The routine uses the method of deflating subspaces, based on
  reordering the eigenvalues in a generalized Schur matrix pair.

  It is assumed that E is nonsingular, but this condition is not
  checked. Note that the definition (1) of the continuous-time
  algebraic Riccati equation, and the formula for the corresponding
  optimal gain matrix, require R to be nonsingular, but the
  associated linear quadratic optimal problem coul