SciPy

scipy.linalg.solve_continuous_are

scipy.linalg.solve_continuous_are(a, b, q, r, e=None, s=None, balanced=True)[source]

Solves the continuous-time algebraic Riccati equation (CARE).

The CARE is defined as

\[X A + A^H X - X B R^{-1} B^H X + Q = 0\]

The limitations for a solution to exist are :

  • All eigenvalues of \(A\) on the right half plane, should be controllable.
  • The associated hamiltonian pencil (See Notes), should have eigenvalues sufficiently away from the imaginary axis.

Moreover, if e or s is not precisely None, then the generalized version of CARE

\[E^HXA + A^HXE - (E^HXB + S) R^{-1} (B^HXE + S^H) + Q = 0\]

is solved. When omitted, e is assumed to be the identity and s is assumed to be the zero matrix with sizes compatible with a and b respectively.

Parameters:

a : (M, M) array_like

Square matrix

b : (M, N) array_like

Input

q : (M, M) array_like

Input

r : (N, N) array_like

Nonsingular square matrix

e : (M, M) array_like, optional

Nonsingular square matrix

s : (M, N) array_like, optional

Input

balanced : bool, optional

The boolean that indicates whether a balancing step is performed on the data. The default is set to True.

Returns:

x : (M, M) ndarray

Solution to the continuous-time algebraic Riccati equation.

Raises:

LinAlgError

For cases where the stable subspace of the pencil could not be isolated. See Notes section and the references for details.

See also

solve_discrete_are
Solves the discrete-time algebraic Riccati equation

Notes

The equation is solved by forming the extended hamiltonian matrix pencil, as described in [R123], \(H - \lambda J\) given by the block matrices

[ A    0    B ]             [ E   0    0 ]
[-Q  -A^H  -S ] - \lambda * [ 0  E^H   0 ]
[ S^H B^H   R ]             [ 0   0    0 ]

and using a QZ decomposition method.

In this algorithm, the fail conditions are linked to the symmetry of the product \(U_2 U_1^{-1}\) and condition number of \(U_1\). Here, \(U\) is the 2m-by-m matrix that holds the eigenvectors spanning the stable subspace with 2m rows and partitioned into two m-row matrices. See [R123] and [R124] for more details.

In order to improve the QZ decomposition accuracy, the pencil goes through a balancing step where the sum of absolute values of \(H\) and \(J\) entries (after removing the diagonal entries of the sum) is balanced following the recipe given in [R125].

New in version 0.11.0.

References

[R123](1, 2, 3) P. van Dooren , “A Generalized Eigenvalue Approach For Solving Riccati Equations.”, SIAM Journal on Scientific and Statistical Computing, Vol.2(2), DOI: 10.1137/0902010
[R124](1, 2) A.J. Laub, “A Schur Method for Solving Algebraic Riccati Equations.”, Massachusetts Institute of Technology. Laboratory for Information and Decision Systems. LIDS-R ; 859. Available online : http://hdl.handle.net/1721.1/1301
[R125](1, 2) P. Benner, “Symplectic Balancing of Hamiltonian Matrices”, 2001, SIAM J. Sci. Comput., 2001, Vol.22(5), DOI: 10.1137/S1064827500367993