slivingston · Sep 29, 2026 · Sep 13, 2026
diff --git a/control/mateqn.py b/control/mateqn.py
@@ -14,7 +14,7 @@
 
 import numpy as np
 import scipy as sp
-from numpy import eye, finfo, inexact
+from numpy import eye, finfo
 from scipy.linalg import eigvals, solve
 
 from .exception import ControlArgument, ControlDimension, ControlSlycot, \
@@ -81,7 +81,7 @@ def _warn_ill_conditioned_E(E):
 #
 
 
-def lyap(A, Q, C=None, E=None, method=None):
+def lyap(A, Q, C=None, E=None, method=None, symmetric_kwargs=None):
     """Solves the continuous-time Lyapunov equation.
 
     X = lyap(A, Q) solves
@@ -117,6 +117,9 @@ def lyap(A, Q, C=None, E=None, method=None):
         Set the method used for computing the result.  Current methods are
         'slycot' and 'scipy'.  If set to None (default), try 'slycot' first
         and then 'scipy'.
+    symmetric_kwargs : dict, optional
+        Keyword arguments passed to `scipy.linalg.issymmetric` or
+        `scipy.linalg.ishermitian`.
 
     Returns
     -------
@@ -169,7 +172,7 @@ def lyap(A, Q, C=None, E=None, method=None):
     # Solve standard Lyapunov equation
     if C is None and E is None:
         # Check to make sure input matrices are the right shape and type
-        _check_shape(Q, n, n, square=True, symmetric=True, name="Q")
+        _check_shape(Q, n, n, square=True, symmetric=True, name="Q", symmetric_kwargs=symmetric_kwargs)
 
         if method == 'scipy':
             # Solve the Lyapunov equation using SciPy
@@ -197,7 +200,7 @@ def lyap(A, Q, C=None, E=None, method=None):
     # Solve the generalized Lyapunov equation
     elif C is None and E is not None:
         # Check to make sure input matrices are the right shape and type
-        _check_shape(Q, n, n, square=True, symmetric=True, name="Q")
+        _check_shape(Q, n, n, square=True, symmetric=True, name="Q", symmetric_kwargs=symmetric_kwargs)
         _check_shape(E, n, n, square=True, name="E")
 
         if method == 'scipy':
@@ -243,7 +246,7 @@ def lyap(A, Q, C=None, E=None, method=None):
     return X
 
 
-def dlyap(A, Q, C=None, E=None, method=None):
+def dlyap(A, Q, C=None, E=None, method=None, symmetric_kwargs=None):
     """Solves the discrete-time Lyapunov equation.
 
     X = dlyap(A, Q) solves
@@ -279,6 +282,9 @@ def dlyap(A, Q, C=None, E=None, method=None):
         Set the method used for computing the result.  Current methods are
         'slycot' and 'scipy'.  If set to None (default), try 'slycot' first
         and then 'scipy'.
+    symmetric_kwargs : dict, optional
+        Keyword arguments passed to `scipy.linalg.issymmetric` or
+        `scipy.linalg.ishermitian`.
 
     Returns
     -------
@@ -346,7 +352,7 @@ def dlyap(A, Q, C=None, E=None, method=None):
     # Solve standard Lyapunov equation
     if C is None and E is None:
         # Check to make sure input matrices are the right shape and type
-        _check_shape(Q, n, n, square=True, symmetric=True, name="Q")
+        _check_shape(Q, n, n, square=True, symmetric=True, name="Q", symmetric_kwargs=symmetric_kwargs)
 
         if method == 'scipy':
             # Solve the Lyapunov equation using SciPy
@@ -406,7 +412,7 @@ def dlyap(A, Q, C=None, E=None, method=None):
     # Solve the generalized Lyapunov equation
     elif C is None and E is not None:
         # Check to make sure input matrices are the right shape and type
-        _check_shape(Q, n, n, square=True, symmetric=True, name="Q")
+        _check_shape(Q, n, n, square=True, symmetric=True, name="Q", symmetric_kwargs=symmetric_kwargs)
         _check_shape(E, n, n, square=True, name="E")
 
         if method == 'scipy':
@@ -449,8 +455,8 @@ def dlyap(A, Q, C=None, E=None, method=None):
 # Riccati equation solvers care and dare
 #
 
-def care(A, B, Q, R=None, S=None, E=None, stabilizing=True, method=None,
-         _As="A", _Bs="B", _Qs="Q", _Rs="R", _Ss="S", _Es="E"):
+def care(A, B, Q, R=None, S=None, E=None, stabilizing=True, method=None, symmetric_kwargs=None,
+         _As="A", _Bs="B", _Qs="Q", _Rs="R", _Ss="S", _Es="E", ):
     """Solves the continuous-time algebraic Riccati equation.
 
     X, L, G = care(A, B, Q, R=None) solves
@@ -484,6 +490,9 @@ def care(A, B, Q, R=None, S=None, E=None, stabilizing=True, method=None,
         Set the method used for computing the result.  Current methods are
         'slycot' and 'scipy'.  If set to None (default), try 'slycot' first
         and then 'scipy'.
+    symmetric_kwargs : dict, optional
+        Keyword arguments passed to `scipy.linalg.issymmetric` or
+        `scipy.linalg.ishermitian`.
     stabilizing : bool, optional
         If `method` is 'slycot', unstabilized eigenvalues will be returned
         in the initial elements of `L`.  Not supported for 'scipy'.
@@ -518,8 +527,8 @@ def care(A, B, Q, R=None, S=None, E=None, stabilizing=True, method=None,
     # Check to make sure input matrices are the right shape and type
     _check_shape(A, n, n, square=True, name=_As)
     _check_shape(B, n, m, name=_Bs)
-    _check_shape(Q, n, n, square=True, symmetric=True, name=_Qs)
-    _check_shape(R, m, m, square=True, symmetric=True, name=_Rs)
+    _check_shape(Q, n, n, square=True, symmetric=True, name=_Qs, symmetric_kwargs=symmetric_kwargs)
+    _check_shape(R, m, m, square=True, symmetric=True, name=_Rs, symmetric_kwargs=symmetric_kwargs)
 
     # Solve the standard algebraic Riccati equation
     if S is None and E is None:
@@ -605,7 +614,7 @@ def care(A, B, Q, R=None, S=None, E=None, stabilizing=True, method=None,
         # the gain matrix G
         return X, L, G
 
-def dare(A, B, Q, R, S=None, E=None, stabilizing=True, method=None,
+def dare(A, B, Q, R, S=None, E=None, stabilizing=True, method=None, symmetric_kwargs=None,
          _As="A", _Bs="B", _Qs="Q", _Rs="R", _Ss="S", _Es="E"):
     """Solves the discrete-time algebraic Riccati equation.
 
@@ -640,6 +649,9 @@ def dare(A, B, Q, R, S=None, E=None, stabilizing=True, method=None,
         Set the method used for computing the result.  Current methods are
         'slycot' and 'scipy'.  If set to None (default), try 'slycot' first
         and then 'scipy'.
+    symmetric_kwargs : dict, optional
+        Keyword arguments passed to `scipy.linalg.issymmetric` or
+        `scipy.linalg.ishermitian`.
     stabilizing : bool, optional
         If `method` is 'slycot', unstabilized eigenvalues will be returned
         in the initial elements of `L`.  Not supported for 'scipy'.
@@ -674,8 +686,8 @@ def dare(A, B, Q, R, S=None, E=None, stabilizing=True, method=None,
     # Check to make sure input matrices are the right shape and type
     _check_shape(A, n, n, square=True, name=_As)
     _check_shape(B, n, m, name=_Bs)
-    _check_shape(Q, n, n, square=True, symmetric=True, name=_Qs)
-    _check_shape(R, m, m, square=True, symmetric=True, name=_Rs)
+    _check_shape(Q, n, n, square=True, symmetric=True, name=_Qs, symmetric_kwargs=symmetric_kwargs)
+    _check_shape(R, m, m, square=True, symmetric=True, name=_Rs, symmetric_kwargs=symmetric_kwargs)
     if E is not None:
         _check_shape(E, n, n, square=True, name=_Es)
     if S is not None:
@@ -740,7 +752,7 @@ def _slycot_or_scipy(method):
 
 
 # Utility function to check matrix dimensions
-def _check_shape(M, n, m, square=False, symmetric=False, name="??"):
+def _check_shape(M, n, m, square=False, symmetric=False, name="??", symmetric_kwargs=None):
     """Check the shape and properties of a 2D array.
 
     This function can be used to check to make sure a 2D array_like has the
@@ -773,7 +785,7 @@ def _check_shape(M, n, m, square=False, symmetric=False, name="??"):
     if (square or symmetric) and M.shape[0] != M.shape[1]:
         raise ControlDimension("%s must be a square matrix" % name)
 
-    if symmetric and not _is_symmetric(M):
+    if symmetric and not _is_symmetric(M, symmetric_kwargs=symmetric_kwargs):
         raise ControlArgument("%s must be a symmetric matrix" % name)
 
     if M.shape[0] != n or M.shape[1] != m:
@@ -785,10 +797,10 @@ def _check_shape(M, n, m, square=False, symmetric=False, name="??"):
 
 
 # Utility function to check if a matrix is symmetric
-def _is_symmetric(M):
-    M = np.atleast_2d(M)
-    if isinstance(M[0, 0], inexact):
-        eps = finfo(M.dtype).eps
-        return ((M - M.T) < eps).all()
-    else:
-        return (M == M.T).all()
+def _is_symmetric(M, symmetric_kwargs=None):
+    if symmetric_kwargs is None:
+        symmetric_kwargs = {}
+
+    if np.iscomplexobj(M):
+        return sp.linalg.ishermitian(M, **symmetric_kwargs)
+    return sp.linalg.issymmetric(M, **symmetric_kwargs)
diff --git a/control/stochsys.py b/control/stochsys.py
@@ -33,7 +33,7 @@
 
 
 # contributed by Sawyer B. Fuller <minster@uw.edu>
-def lqe(*args, **kwargs):
+def lqe(*args, symmetric_kwargs=None, **kwargs):
     r"""lqe(A, G, C, QN, RN, [, NN])
 
     Continuous-time linear quadratic estimator (Kalman filter).
@@ -83,6 +83,9 @@ def lqe(*args, **kwargs):
         Set the method used for computing the result.  Current methods are
         'slycot' and 'scipy'.  If set to None (default), try 'slycot' first
         and then 'scipy'.
+    symmetric_kwargs : dict, optional
+        Keyword arguments passed to `scipy.linalg.issymmetric` or
+        `scipy.linalg.ishermitian`.
 
     Returns
     -------
@@ -178,12 +181,12 @@ def lqe(*args, **kwargs):
 
     # Compute the result (dimension and symmetry checking done in care())
     P, E, LT = care(A.T, C.T, G @ QN @ G.T, RN, method=method,
-                    _Bs="C", _Qs="QN", _Rs="RN", _Ss="NN")
+                    _Bs="C", _Qs="QN", _Rs="RN", _Ss="NN", symmetric_kwargs=symmetric_kwargs)
     return LT.T, P, E
 
 
 # contributed by Sawyer B. Fuller <minster@uw.edu>
-def dlqe(*args, **kwargs):
+def dlqe(*args, symmetric_kwargs=None, **kwargs):
     r"""dlqe(A, G, C, QN, RN, [, N])
 
     Discrete-time linear quadratic estimator (Kalman filter).
@@ -220,6 +223,9 @@ def dlqe(*args, **kwargs):
         Set the method used for computing the result.  Current methods are
         'slycot' and 'scipy'.  If set to None (default), try 'slycot'
         first and then 'scipy'.
+    symmetric_kwargs : dict, optional
+        Keyword arguments passed to `scipy.linalg.issymmetric` or
+        `scipy.linalg.ishermitian`.
 
     Returns
     -------
@@ -299,7 +305,7 @@ def dlqe(*args, **kwargs):
 
     # Compute the result (dimension and symmetry checking done in dare())
     P, E, LT = dare(A.T, C.T, G @ QN @ G.T, RN, method=method,
-                    _Bs="C", _Qs="QN", _Rs="RN", _Ss="NN")
+                    _Bs="C", _Qs="QN", _Rs="RN", _Ss="NN", symmetric_kwargs=symmetric_kwargs)
     return LT.T, P, E
 
 
@@ -312,7 +318,7 @@ def create_estimator_iosystem(
         control_indices=None, disturbance_indices=None,
         estimate_labels='xhat[{i}]', covariance_labels='P[{i},{j}]',
         measurement_labels=None, control_labels=None,
-        inputs=None, outputs=None, states=None, **kwargs):
+        inputs=None, outputs=None, states=None, symmetric_kwargs=None, **kwargs):
     r"""Create an I/O system implementing a linear quadratic estimator.
 
     This function creates an input/output system that implements a
@@ -410,6 +416,9 @@ def create_estimator_iosystem(
     name : string, optional
         System name (used for specifying signals). If unspecified, a generic
         name 'sys[id]' is generated with a unique integer id.
+    symmetric_kwargs : dict, optional
+        Keyword arguments passed to `scipy.linalg.issymmetric` or
+        `scipy.linalg.ishermitian`.
 
     Notes
     -----
@@ -492,7 +501,7 @@ def create_estimator_iosystem(
     if P0 is None:
         # Initialize P0 to the steady state value
         _, P0, _ = lqe(A, G, C, QN, RN)
-    P0 = _check_shape(P0, sys.nstates, sys.nstates, symmetric=True, name='P0')
+    P0 = _check_shape(P0, sys.nstates, sys.nstates, symmetric=True, name='P0', symmetric_kwargs=symmetric_kwargs)
 
     # Figure out the labels to use
     estimate_labels = _process_labels(

diff --git a/control/tests/mateqn_test.py b/control/tests/mateqn_test.py
@@ -39,7 +39,7 @@
 import pytest
 from scipy.linalg import eigvals, solve
 
-from control.mateqn import lyap, dlyap, care, dare
+from control.mateqn import lyap, dlyap, care, dare, _is_symmetric
 from control.exception import ControlArgument, ControlDimension
 
 
@@ -466,3 +466,25 @@ def test_raise(self):
                 cdare(A, B, Qfs, R, S, E)
             with pytest.raises(ControlArgument):
                 cdare(A, B, Q, Rfs, S, E)
+
+    def test_is_symmetric_scale_aware(self):
+        M = np.array([
+            [1e8, 1e8],
+            [1e8 + 1e-8, 1e8]
+        ])
+        assert not _is_symmetric(M)
+        assert _is_symmetric(M,symmetric_kwargs={"rtol": 1e-12},)
+
+    def test_is_symmetric_rejects_asymmetric(self):
+        M = np.array([
+            [1., 2.],
+            [5., 1.]
+        ])
+        assert not _is_symmetric(M)
+
+    def test_is_symmetric_complex_hermitian(self):
+        M = np.array([
+            [1., 2. + 1.j],
+            [2. - 1.j, 3.]
+        ])
+        assert _is_symmetric(M)
diff --git a/control/tests/stochsys_test.py b/control/tests/stochsys_test.py
@@ -35,6 +35,54 @@ def test_LQE(method):
     L, P, poles = lqe(A, G, C, QN, RN, method=method)
     check_LQE(L, P, poles, G, QN, RN)
 
+def test_lqe_symmetric_kwargs():
+    A = np.array([
+        [-1., 0.],
+        [0., -2.]
+    ])
+    G = np.eye(2)
+    C = np.eye(2)
+    QN = np.array([
+        [1., 0.2],
+        [0.2 + 1e-15, 1.]
+    ])
+    RN = np.eye(2)
+
+    # Exact symmetry check should fail
+    with pytest.raises(ControlArgument, match="symmetric"):
+        lqe(A, G, C, QN, RN, method="scipy")
+
+    # Passing rtol should allow the nearly symmetric matrix
+    lqe(
+        A, G, C, QN, RN,
+        method="scipy",
+        symmetric_kwargs={"rtol": 1e-12},
+    )
+
+def test_dlqe_symmetric_kwargs():
+    A = np.array([
+        [0.5, 0.],
+        [0., 0.4]
+    ])
+    G = np.eye(2)
+    C = np.eye(2)
+    QN = np.array([
+        [1., 0.2],
+        [0.2 + 1e-15, 1.]
+    ])
+    RN = np.eye(2)
+
+    # Exact symmetry check should fail
+    with pytest.raises(ControlArgument, match="symmetric"):
+        dlqe(A, G, C, QN, RN, method="scipy")
+
+    # Passing rtol should allow the nearly symmetric matrix
+    dlqe(
+        A, G, C, QN, RN,
+        method="scipy",
+        symmetric_kwargs={"rtol": 1e-12},
+    )
+
 @pytest.mark.parametrize("cdlqe", [lqe, dlqe])
 def test_lqe_call_format(cdlqe):
     # Create a random state space system for testing