From e8e87a47e045739c08aea6c7e0dc91eb1ee24b7e Mon Sep 17 00:00:00 2001
From: Mark <myeatman@oxefit.com>
Date: Mon, 30 May 2022 22:44:56 -0500
Subject: [PATCH 01/20] Add passivity module, is_passive function, and
 passivity_test.

---
 control/passivity.py            | 54 +++++++++++++++++++++++++++++++++
 control/tests/passivity_test.py | 25 +++++++++++++++
 2 files changed, 79 insertions(+)
 create mode 100644 control/passivity.py
 create mode 100644 control/tests/passivity_test.py

diff --git a/control/passivity.py b/control/passivity.py
new file mode 100644
index 000000000..f33f7ff09
--- /dev/null
+++ b/control/passivity.py
@@ -0,0 +1,54 @@
+'''
+Author: Mark Yeatman  
+Date: May 15, 2022
+'''
+
+from . import statesp as ss
+from sympy import symbols, Matrix, symarray
+from lmi_sdp import LMI_NSD, to_cvxopt
+from cvxopt import solvers
+
+import numpy as np
+
+
+def is_passive(sys):
+    '''
+    Indicates if a linear time invarient system is passive
+
+    Constructs a linear matrix inequality and a feasibility optimization
+    such that is a solution exists, the system is passive.
+
+    The source for the algorithm is: 
+    McCourt, Michael J., and Panos J. Antsaklis. "Demonstrating passivity and dissipativity using computational methods." ISIS 8 (2013).
+    '''
+
+    A = sys.A
+    B = sys.B
+    C = sys.C
+    D = sys.D
+
+    P = Matrix(symarray('p', A.shape))
+
+    # enforce symmetry in P
+    size = A.shape[0]
+    for i in range(0, size):
+        for j in range(0, size):
+            P[i, j] = P[j, i]
+
+    # construct matrix for storage function x'*V*x
+    V = Matrix.vstack(
+        Matrix.hstack(A.T * P + P*A, P*B - C.T),
+        Matrix.hstack(B.T*P - C, Matrix(-D - D.T))
+    )
+
+    # construct LMI, convert to form for feasibility solver
+    LMI_passivty = LMI_NSD(V, 0*V)
+    min_obj = 0 * symbols("x")
+    variables = V.free_symbols
+    solvers.options['show_progress'] = False
+    c, Gs, hs = to_cvxopt(min_obj, LMI_passivty, variables)
+
+    # crunch feasibility solution
+    sol = solvers.sdp(c, Gs=Gs, hs=hs)
+
+    return (sol["x"] is not None)
diff --git a/control/tests/passivity_test.py b/control/tests/passivity_test.py
new file mode 100644
index 000000000..5041c4695
--- /dev/null
+++ b/control/tests/passivity_test.py
@@ -0,0 +1,25 @@
+'''
+Author: Mark Yeatman  
+Date: May 30, 2022
+'''
+
+import pytest
+import numpy
+from control import ss, passivity
+from sympy import Matrix
+
+
+def test_is_passive():
+    A = numpy.array([[0, 1], [-2, -2]])
+    B = numpy.array([[0], [1]])
+    C = numpy.array([[-1, 2]])
+    D = numpy.array([[1.5]])
+    sys = ss(A, B, C, D)
+
+    assert(passivity.is_passive(sys))
+
+    D = -D
+    sys = ss(A, B, C, D)
+
+    assert(not passivity.is_passive(sys))
+

From 2eef6612a046b2982327a36ffe03beb4a0aa54f3 Mon Sep 17 00:00:00 2001
From: Mark <myeatman@oxefit.com>
Date: Mon, 6 Jun 2022 14:32:02 -0500
Subject: [PATCH 02/20] Remove dependancies on lmi-sdp and sympy for
 is_passive.

---
 control/passivity.py | 53 +++++++++++++++++++++++++-------------------
 1 file changed, 30 insertions(+), 23 deletions(-)

diff --git a/control/passivity.py b/control/passivity.py
index f33f7ff09..12c2c8ad7 100644
--- a/control/passivity.py
+++ b/control/passivity.py
@@ -4,11 +4,8 @@
 '''
 
 from . import statesp as ss
-from sympy import symbols, Matrix, symarray
-from lmi_sdp import LMI_NSD, to_cvxopt
-from cvxopt import solvers
-
 import numpy as np
+import cvxopt as cvx
 
 
 def is_passive(sys):
@@ -27,28 +24,38 @@ def is_passive(sys):
     C = sys.C
     D = sys.D
 
-    P = Matrix(symarray('p', A.shape))
-
-    # enforce symmetry in P
-    size = A.shape[0]
-    for i in range(0, size):
-        for j in range(0, size):
-            P[i, j] = P[j, i]
-
-    # construct matrix for storage function x'*V*x
-    V = Matrix.vstack(
-        Matrix.hstack(A.T * P + P*A, P*B - C.T),
-        Matrix.hstack(B.T*P - C, Matrix(-D - D.T))
+    def make_LMI_matrix(P):
+        V = np.vstack((
+            np.hstack((A.T @ P + P@A, P@B)),
+            np.hstack((B.T@P, np.zeros_like(D))))
+        )
+        return V
+
+    P = np.zeros_like(A)
+    matrix_list = []
+    state_space_size = A.shape[0]
+    for i in range(0, state_space_size):
+        for j in range(0, state_space_size):
+            if j <= i:
+                P = P*0.0
+                P[i, j] = 1.0
+                P[j, i] = 1.0
+                matrix_list.append(make_LMI_matrix(P).flatten())
+
+    coefficents = np.vstack(matrix_list).T
+
+    constants = -np.vstack((
+        np.hstack((np.zeros_like(A),  - C.T)),
+        np.hstack((- C, -D - D.T)))
     )
 
-    # construct LMI, convert to form for feasibility solver
-    LMI_passivty = LMI_NSD(V, 0*V)
-    min_obj = 0 * symbols("x")
-    variables = V.free_symbols
-    solvers.options['show_progress'] = False
-    c, Gs, hs = to_cvxopt(min_obj, LMI_passivty, variables)
+    number_of_opt_vars = int(
+        (state_space_size**2-state_space_size)/2 + state_space_size)
+    c = cvx.matrix(0.0, (number_of_opt_vars, 1))
 
     # crunch feasibility solution
-    sol = solvers.sdp(c, Gs=Gs, hs=hs)
+    sol = cvx.solvers.sdp(c,
+                          Gs=[cvx.matrix(coefficents)],
+                          hs=[cvx.matrix(constants)])
 
     return (sol["x"] is not None)

From 147a24ea0ba9da03b3774b7993e20e785776e027 Mon Sep 17 00:00:00 2001
From: Mark <myeatman@oxefit.com>
Date: Mon, 6 Jun 2022 14:37:53 -0500
Subject: [PATCH 03/20] Use sys.nstates in stead of using A.shape[0]

---
 control/passivity.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/control/passivity.py b/control/passivity.py
index 12c2c8ad7..2bc00f958 100644
--- a/control/passivity.py
+++ b/control/passivity.py
@@ -33,7 +33,7 @@ def make_LMI_matrix(P):
 
     P = np.zeros_like(A)
     matrix_list = []
-    state_space_size = A.shape[0]
+    state_space_size = sys.nstates
     for i in range(0, state_space_size):
         for j in range(0, state_space_size):
             if j <= i:

From fdb2d4ad6bf15d7565347528a69a99ce4e121fda Mon Sep 17 00:00:00 2001
From: Mark <myeatman@oxefit.com>
Date: Mon, 6 Jun 2022 14:58:51 -0500
Subject: [PATCH 04/20] Attempt to setup cvxopt similar to slycot.

---
 .github/workflows/python-package-conda.yml |  4 ++++
 control/exception.py                       | 12 ++++++++++++
 control/tests/conftest.py                  |  2 ++
 control/tests/passivity_test.py            |  4 ++--
 setup.py                                   |  3 ++-
 5 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/.github/workflows/python-package-conda.yml b/.github/workflows/python-package-conda.yml
index 3f1910697..e4b1aea42 100644
--- a/.github/workflows/python-package-conda.yml
+++ b/.github/workflows/python-package-conda.yml
@@ -13,6 +13,7 @@ jobs:
         python-version: [3.7, 3.9]
         slycot: ["", "conda"]
         pandas: [""]
+        cvxopt: ["conda"]
         array-and-matrix: [0]
         include:
           - python-version: 3.9
@@ -46,6 +47,9 @@ jobs:
         if [[ '${{matrix.pandas}}' == 'conda' ]]; then
           conda install -c conda-forge pandas
         fi
+        if [[ '${{matrix.cvxopt}}' == 'conda' ]]; then
+          conda install -c conda-forge cvxopt
+        fi
 
     - name: Test with pytest
       env:
diff --git a/control/exception.py b/control/exception.py
index f66eb7f30..d14ff87e6 100644
--- a/control/exception.py
+++ b/control/exception.py
@@ -84,3 +84,15 @@ def pandas_check():
         except:
             pandas_installed = False
     return pandas_installed
+
+# Utility function to see if cvxopt is installed
+cvxopt_installed = None
+def cvxopt_check():
+    global cvxopt_installed
+    if cvxopt_installed is None:
+        try:
+            import cvxopt
+            cvxopt_installed = True
+        except:
+            cvxopt_installed = False
+    return cvxopt_installed
\ No newline at end of file
diff --git a/control/tests/conftest.py b/control/tests/conftest.py
index b67ef3674..853c1dd61 100644
--- a/control/tests/conftest.py
+++ b/control/tests/conftest.py
@@ -18,6 +18,8 @@
 # pytest.param(marks=)
 slycotonly = pytest.mark.skipif(not control.exception.slycot_check(),
                                 reason="slycot not installed")
+cvxoptonly = pytest.mark.skipif(not control.exception.cvxopt_check(),
+                                reason="cvxopt not installed")
 noscipy0 = pytest.mark.skipif(StrictVersion(sp.__version__) < "1.0",
                               reason="requires SciPy 1.0 or greater")
 nopython2 = pytest.mark.skipif(sys.version_info < (3, 0),
diff --git a/control/tests/passivity_test.py b/control/tests/passivity_test.py
index 5041c4695..182e3923f 100644
--- a/control/tests/passivity_test.py
+++ b/control/tests/passivity_test.py
@@ -3,12 +3,12 @@
 Date: May 30, 2022
 '''
 
-import pytest
 import numpy
 from control import ss, passivity
 from sympy import Matrix
+from control.tests.conftest import cvxoptonly
 
-
+@cvxoptonly
 def test_is_passive():
     A = numpy.array([[0, 1], [-2, -2]])
     B = numpy.array([[0], [1]])
diff --git a/setup.py b/setup.py
index f5e766ebb..58e4d11cf 100644
--- a/setup.py
+++ b/setup.py
@@ -43,6 +43,7 @@
                       'matplotlib'],
     extras_require={
        'test': ['pytest', 'pytest-timeout'],
-       'slycot': [ 'slycot>=0.4.0' ]
+       'slycot': [ 'slycot>=0.4.0' ],
+       'cvxopt': [ 'cvxopt>=1.2.0' ]
     }
 )

From dc46f3cf2c70a884661a1dbd2fa274ee99083c87 Mon Sep 17 00:00:00 2001
From: Mark <mark.x.yeatman@gmail.com>
Date: Tue, 7 Jun 2022 11:48:36 -0400
Subject: [PATCH 05/20] Remove unused import.

---
 control/passivity.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/control/passivity.py b/control/passivity.py
index 2bc00f958..f37443722 100644
--- a/control/passivity.py
+++ b/control/passivity.py
@@ -3,7 +3,6 @@
 Date: May 15, 2022
 '''
 
-from . import statesp as ss
 import numpy as np
 import cvxopt as cvx
 

From 0ecc1354765cc7753d8a980ea2e70c9be79186b6 Mon Sep 17 00:00:00 2001
From: Mark <mark.x.yeatman@gmail.com>
Date: Tue, 7 Jun 2022 11:49:47 -0400
Subject: [PATCH 06/20] Apply suggestions from code review

Co-authored-by: Ben Greiner <code@bnavigator.de>
---
 .github/workflows/python-package-conda.yml | 2 +-
 control/exception.py                       | 2 +-
 control/tests/passivity_test.py            | 1 -
 3 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/.github/workflows/python-package-conda.yml b/.github/workflows/python-package-conda.yml
index e4b1aea42..c0e720ea8 100644
--- a/.github/workflows/python-package-conda.yml
+++ b/.github/workflows/python-package-conda.yml
@@ -13,7 +13,7 @@ jobs:
         python-version: [3.7, 3.9]
         slycot: ["", "conda"]
         pandas: [""]
-        cvxopt: ["conda"]
+        cvxopt: ["", "conda"]
         array-and-matrix: [0]
         include:
           - python-version: 3.9
diff --git a/control/exception.py b/control/exception.py
index d14ff87e6..575c78c0a 100644
--- a/control/exception.py
+++ b/control/exception.py
@@ -95,4 +95,4 @@ def cvxopt_check():
             cvxopt_installed = True
         except:
             cvxopt_installed = False
-    return cvxopt_installed
\ No newline at end of file
+    return cvxopt_installed
diff --git a/control/tests/passivity_test.py b/control/tests/passivity_test.py
index 182e3923f..947b5729c 100644
--- a/control/tests/passivity_test.py
+++ b/control/tests/passivity_test.py
@@ -5,7 +5,6 @@
 
 import numpy
 from control import ss, passivity
-from sympy import Matrix
 from control.tests.conftest import cvxoptonly
 
 @cvxoptonly

From 649b21ee7e915fc8758413da04f4ec411ba58d61 Mon Sep 17 00:00:00 2001
From: Mark <mark.x.yeatman@gmail.com>
Date: Tue, 7 Jun 2022 12:07:45 -0400
Subject: [PATCH 07/20] Update passivity.py

---
 control/passivity.py | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/control/passivity.py b/control/passivity.py
index f37443722..17a64120d 100644
--- a/control/passivity.py
+++ b/control/passivity.py
@@ -4,8 +4,11 @@
 '''
 
 import numpy as np
-import cvxopt as cvx
 
+try:
+    import cvxopt as cvx
+except ImportError as e:
+    cvx = None
 
 def is_passive(sys):
     '''
@@ -17,7 +20,9 @@ def is_passive(sys):
     The source for the algorithm is: 
     McCourt, Michael J., and Panos J. Antsaklis. "Demonstrating passivity and dissipativity using computational methods." ISIS 8 (2013).
     '''
-
+    if cvx is None:
+        raise ModuleNotFoundError
+    
     A = sys.A
     B = sys.B
     C = sys.C

From b73e6fe0eac04fc541056d3ee9430c767b6d126b Mon Sep 17 00:00:00 2001
From: Mark <myeatman@oxefit.com>
Date: Mon, 13 Jun 2022 14:19:36 -0500
Subject: [PATCH 08/20] Address some review comments.

---
 .github/workflows/python-package-conda.yml |  2 +-
 control/passivity.py                       | 10 ++++++----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/.github/workflows/python-package-conda.yml b/.github/workflows/python-package-conda.yml
index c0e720ea8..d8f810104 100644
--- a/.github/workflows/python-package-conda.yml
+++ b/.github/workflows/python-package-conda.yml
@@ -4,7 +4,7 @@ on: [push, pull_request]
 
 jobs:
   test-linux:
-    name: Python ${{ matrix.python-version }}${{ matrix.slycot && format(' with Slycot from {0}', matrix.slycot) || ' without Slycot' }}${{ matrix.pandas && ', with pandas' || '' }}${{ matrix.array-and-matrix == 1 && ', array and matrix' || '' }}
+    name: Python ${{ matrix.python-version }}${{ matrix.slycot && format(' with Slycot from {0}', matrix.slycot) || ' without Slycot' }}${{ matrix.pandas && ', with pandas' || '' }}${{ matrix.array-and-matrix == 1 && ', array and matrix' || '' }}${{ matrix.cvxopt && format(' with cvxopt from {0}', matrix.cvxopt) || ' without cvxopt' }}
     runs-on: ubuntu-latest
 
     strategy:
diff --git a/control/passivity.py b/control/passivity.py
index 17a64120d..109a75356 100644
--- a/control/passivity.py
+++ b/control/passivity.py
@@ -10,6 +10,7 @@
 except ImportError as e:
     cvx = None
 
+
 def is_passive(sys):
     '''
     Indicates if a linear time invarient system is passive
@@ -18,11 +19,13 @@ def is_passive(sys):
     such that is a solution exists, the system is passive.
 
     The source for the algorithm is: 
-    McCourt, Michael J., and Panos J. Antsaklis. "Demonstrating passivity and dissipativity using computational methods." ISIS 8 (2013).
+    McCourt, Michael J., and Panos J. Antsaklis. 
+        "Demonstrating passivity and dissipativity using computational methods." ISIS 8 (2013).
     '''
     if cvx is None:
+        print("cvxopt required for passivity module")
         raise ModuleNotFoundError
-    
+
     A = sys.A
     B = sys.B
     C = sys.C
@@ -35,13 +38,12 @@ def make_LMI_matrix(P):
         )
         return V
 
-    P = np.zeros_like(A)
     matrix_list = []
     state_space_size = sys.nstates
     for i in range(0, state_space_size):
         for j in range(0, state_space_size):
             if j <= i:
-                P = P*0.0
+                P = np.zeros_like(A)
                 P[i, j] = 1.0
                 P[j, i] = 1.0
                 matrix_list.append(make_LMI_matrix(P).flatten())

From cd7ec0fce4cc73954d2c3769adff0373b9ef62b2 Mon Sep 17 00:00:00 2001
From: Mark <mark.x.yeatman@gmail.com>
Date: Mon, 13 Jun 2022 14:56:35 -0500
Subject: [PATCH 09/20] Update control/passivity.py

Co-authored-by: Ben Greiner <code@bnavigator.de>
---
 control/passivity.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/control/passivity.py b/control/passivity.py
index 109a75356..3d376f392 100644
--- a/control/passivity.py
+++ b/control/passivity.py
@@ -24,7 +24,7 @@ def is_passive(sys):
     '''
     if cvx is None:
         print("cvxopt required for passivity module")
-        raise ModuleNotFoundError
+        raise ModuleNotFoundError("cvxopt required for passivity module")
 
     A = sys.A
     B = sys.B

From d65f1d230baa84cf3c74378a1505f6eea5093439 Mon Sep 17 00:00:00 2001
From: Mark <myeatman@oxefit.com>
Date: Mon, 13 Jun 2022 15:01:52 -0500
Subject: [PATCH 10/20] Remove duplicate "print" statement.

---
 control/passivity.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/control/passivity.py b/control/passivity.py
index 3d376f392..a87e07730 100644
--- a/control/passivity.py
+++ b/control/passivity.py
@@ -23,7 +23,6 @@ def is_passive(sys):
         "Demonstrating passivity and dissipativity using computational methods." ISIS 8 (2013).
     '''
     if cvx is None:
-        print("cvxopt required for passivity module")
         raise ModuleNotFoundError("cvxopt required for passivity module")
 
     A = sys.A

From 7e79c822d069ba13c77c210c4a9975168bea3b3b Mon Sep 17 00:00:00 2001
From: Mark <myeatman@oxefit.com>
Date: Mon, 13 Jun 2022 15:36:56 -0500
Subject: [PATCH 11/20] Fix grammar in doc string.

---
 control/passivity.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/control/passivity.py b/control/passivity.py
index a87e07730..df99ee20c 100644
--- a/control/passivity.py
+++ b/control/passivity.py
@@ -16,7 +16,7 @@ def is_passive(sys):
     Indicates if a linear time invarient system is passive
 
     Constructs a linear matrix inequality and a feasibility optimization
-    such that is a solution exists, the system is passive.
+    such that if a solution exists, the system is passive.
 
     The source for the algorithm is: 
     McCourt, Michael J., and Panos J. Antsaklis. 

From c57b928528df7573d47651abc8db9043a2e26d5c Mon Sep 17 00:00:00 2001
From: Mark <myeatman@oxefit.com>
Date: Mon, 13 Jun 2022 17:08:48 -0500
Subject: [PATCH 12/20] Another grammar in doc string fix.

---
 control/passivity.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/control/passivity.py b/control/passivity.py
index df99ee20c..ad032d60b 100644
--- a/control/passivity.py
+++ b/control/passivity.py
@@ -13,7 +13,7 @@
 
 def is_passive(sys):
     '''
-    Indicates if a linear time invarient system is passive
+    Indicates if a linear time invariant system is passive
 
     Constructs a linear matrix inequality and a feasibility optimization
     such that if a solution exists, the system is passive.

From 27487a9707d0ea28e41358f36e815eff792a2990 Mon Sep 17 00:00:00 2001
From: Mark <myeatman@oxefit.com>
Date: Mon, 13 Jun 2022 19:39:29 -0500
Subject: [PATCH 13/20] Address edge case of stricly proper systems.

---
 control/passivity.py            |  6 ++++++
 control/tests/passivity_test.py | 12 ++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/control/passivity.py b/control/passivity.py
index ad032d60b..1d981c9de 100644
--- a/control/passivity.py
+++ b/control/passivity.py
@@ -10,6 +10,7 @@
 except ImportError as e:
     cvx = None
 
+lmi_epsilon = 1e-12
 
 def is_passive(sys):
     '''
@@ -30,6 +31,10 @@ def is_passive(sys):
     C = sys.C
     D = sys.D
 
+    #account for strictly proper systems
+    [n,m] = D.shape
+    D = D + np.nextafter(0,1)*np.eye(n,m)
+
     def make_LMI_matrix(P):
         V = np.vstack((
             np.hstack((A.T @ P + P@A, P@B)),
@@ -59,6 +64,7 @@ def make_LMI_matrix(P):
     c = cvx.matrix(0.0, (number_of_opt_vars, 1))
 
     # crunch feasibility solution
+    cvx.solvers.options['show_progress'] = False
     sol = cvx.solvers.sdp(c,
                           Gs=[cvx.matrix(coefficents)],
                           hs=[cvx.matrix(constants)])
diff --git a/control/tests/passivity_test.py b/control/tests/passivity_test.py
index 947b5729c..79197866f 100644
--- a/control/tests/passivity_test.py
+++ b/control/tests/passivity_test.py
@@ -15,10 +15,22 @@ def test_is_passive():
     D = numpy.array([[1.5]])
     sys = ss(A, B, C, D)
 
+    # happy path is passive
     assert(passivity.is_passive(sys))
 
+    # happy path not passive
     D = -D
     sys = ss(A, B, C, D)
 
     assert(not passivity.is_passive(sys))
 
+    #edge cases of D=0 boundary condition
+    B *= 0
+    C *= 0
+    D *= 0
+    sys = ss(A, B, C, D)
+    assert(passivity.is_passive(sys))
+
+    A = A*1e12
+    sys = ss(A, B, C, D)
+    assert(passivity.is_passive(sys))
\ No newline at end of file

From d6916c661a7799e5998f84f5e2d34368ace528a8 Mon Sep 17 00:00:00 2001
From: Mark <myeatman@oxefit.com>
Date: Tue, 14 Jun 2022 06:46:56 -0500
Subject: [PATCH 14/20] Expand unit tests, add info to doc string for
 parameters and returns, rename is_passive to ispassive for naming convention
 consistency. Autoformat to pep8.

---
 control/passivity.py            | 21 +++++++++++-----
 control/tests/passivity_test.py | 43 +++++++++++++++++++++++++++------
 2 files changed, 50 insertions(+), 14 deletions(-)

diff --git a/control/passivity.py b/control/passivity.py
index 1d981c9de..b00cc6b65 100644
--- a/control/passivity.py
+++ b/control/passivity.py
@@ -10,11 +10,10 @@
 except ImportError as e:
     cvx = None
 
-lmi_epsilon = 1e-12
 
-def is_passive(sys):
+def ispassive(sys):
     '''
-    Indicates if a linear time invariant system is passive
+    Indicates if a linear time invariant (LTI) system is passive
 
     Constructs a linear matrix inequality and a feasibility optimization
     such that if a solution exists, the system is passive.
@@ -22,6 +21,16 @@ def is_passive(sys):
     The source for the algorithm is: 
     McCourt, Michael J., and Panos J. Antsaklis. 
         "Demonstrating passivity and dissipativity using computational methods." ISIS 8 (2013).
+
+    Parameters
+    ----------
+    sys: A continuous LTI system
+        System to be checked.
+
+    Returns
+    -------
+    bool: 
+        The input system passive.
     '''
     if cvx is None:
         raise ModuleNotFoundError("cvxopt required for passivity module")
@@ -31,9 +40,9 @@ def is_passive(sys):
     C = sys.C
     D = sys.D
 
-    #account for strictly proper systems
-    [n,m] = D.shape
-    D = D + np.nextafter(0,1)*np.eye(n,m)
+    # account for strictly proper systems
+    [n, m] = D.shape
+    D = D + np.nextafter(0, 1)*np.eye(n, m)
 
     def make_LMI_matrix(P):
         V = np.vstack((
diff --git a/control/tests/passivity_test.py b/control/tests/passivity_test.py
index 79197866f..171d3c542 100644
--- a/control/tests/passivity_test.py
+++ b/control/tests/passivity_test.py
@@ -7,8 +7,9 @@
 from control import ss, passivity
 from control.tests.conftest import cvxoptonly
 
+
 @cvxoptonly
-def test_is_passive():
+def test_ispassive():
     A = numpy.array([[0, 1], [-2, -2]])
     B = numpy.array([[0], [1]])
     C = numpy.array([[-1, 2]])
@@ -16,21 +17,47 @@ def test_is_passive():
     sys = ss(A, B, C, D)
 
     # happy path is passive
-    assert(passivity.is_passive(sys))
+    assert(passivity.ispassive(sys))
 
     # happy path not passive
     D = -D
     sys = ss(A, B, C, D)
 
-    assert(not passivity.is_passive(sys))
+    assert(not passivity.ispassive(sys))
+
+
+@cvxoptonly
+def test_ispassive_edge_cases():
+    A = numpy.array([[0, 1], [-2, -2]])
+    B = numpy.array([[0], [1]])
+    C = numpy.array([[-1, 2]])
+    D = numpy.array([[1.5]])
 
-    #edge cases of D=0 boundary condition
-    B *= 0
-    C *= 0
     D *= 0
+
+    # strictly proper
     sys = ss(A, B, C, D)
-    assert(passivity.is_passive(sys))
+    assert(passivity.ispassive(sys))
 
+    # ill conditioned
     A = A*1e12
     sys = ss(A, B, C, D)
-    assert(passivity.is_passive(sys))
\ No newline at end of file
+    assert(passivity.ispassive(sys))
+
+    # different combinations of zero A,B,C,D are 0
+    B *= 0
+    C *= 0
+    assert(passivity.ispassive(sys))
+
+    A *= 0
+    B = numpy.array([[0], [1]])
+    C = numpy.array([[-1, 2]])
+    D = numpy.array([[1.5]])
+    assert(passivity.ispassive(sys))
+
+    B *= 0
+    C *= 0
+    assert(passivity.ispassive(sys))
+
+    A *= 0
+    assert(passivity.ispassive(sys))

From bb16be01ff70919971d990a3228b6ff96b9b8182 Mon Sep 17 00:00:00 2001
From: mark-yeatman <mark.x.yeatman@gmail.com>
Date: Tue, 14 Jun 2022 11:26:30 -0400
Subject: [PATCH 15/20] Parameterize unit tests. Catch edge case of A=0.

---
 control/passivity.py            |  7 +++--
 control/tests/passivity_test.py | 53 +++++++++++++--------------------
 2 files changed, 25 insertions(+), 35 deletions(-)

diff --git a/control/passivity.py b/control/passivity.py
index b00cc6b65..b2cf5a09e 100644
--- a/control/passivity.py
+++ b/control/passivity.py
@@ -44,6 +44,9 @@ def ispassive(sys):
     [n, m] = D.shape
     D = D + np.nextafter(0, 1)*np.eye(n, m)
 
+    [n, _] = A.shape
+    A = A - np.nextafter(0, 1)*np.eye(n)
+
     def make_LMI_matrix(P):
         V = np.vstack((
             np.hstack((A.T @ P + P@A, P@B)),
@@ -75,7 +78,7 @@ def make_LMI_matrix(P):
     # crunch feasibility solution
     cvx.solvers.options['show_progress'] = False
     sol = cvx.solvers.sdp(c,
-                          Gs=[cvx.matrix(coefficents)],
-                          hs=[cvx.matrix(constants)])
+                        Gs=[cvx.matrix(coefficents)],
+                        hs=[cvx.matrix(constants)])
 
     return (sol["x"] is not None)
diff --git a/control/tests/passivity_test.py b/control/tests/passivity_test.py
index 171d3c542..d413f6fa5 100644
--- a/control/tests/passivity_test.py
+++ b/control/tests/passivity_test.py
@@ -2,7 +2,7 @@
 Author: Mark Yeatman  
 Date: May 30, 2022
 '''
-
+import pytest
 import numpy
 from control import ss, passivity
 from control.tests.conftest import cvxoptonly
@@ -25,39 +25,26 @@ def test_ispassive():
 
     assert(not passivity.ispassive(sys))
 
-
+A_d = numpy.array([[-2, 0], [0, 0]])
+A = numpy.array([[-3, 0], [0, -2]])
+B = numpy.array([[0], [1]])
+C = numpy.array([[-1, 2]])
+D = numpy.array([[1.5]])
 @cvxoptonly
-def test_ispassive_edge_cases():
-    A = numpy.array([[0, 1], [-2, -2]])
-    B = numpy.array([[0], [1]])
-    C = numpy.array([[-1, 2]])
-    D = numpy.array([[1.5]])
-
-    D *= 0
+@pytest.mark.parametrize(
+    "test_input,expected", 
+    [((A,B,C,D*0.0), True), 
+     ((A_d,B,C,D), True), 
+     ((A*1e12,B,C,D*0), True), 
+     ((A,B*0,C*0,D), True),
+     ((A*0,B,C,D), True),
+     ((A*0,B*0,C*0,D*0), True)])
+def test_ispassive_edge_cases(test_input, expected):
 
     # strictly proper
+    A = test_input[0]
+    B = test_input[1]
+    C = test_input[2]
+    D = test_input[3]
     sys = ss(A, B, C, D)
-    assert(passivity.ispassive(sys))
-
-    # ill conditioned
-    A = A*1e12
-    sys = ss(A, B, C, D)
-    assert(passivity.ispassive(sys))
-
-    # different combinations of zero A,B,C,D are 0
-    B *= 0
-    C *= 0
-    assert(passivity.ispassive(sys))
-
-    A *= 0
-    B = numpy.array([[0], [1]])
-    C = numpy.array([[-1, 2]])
-    D = numpy.array([[1.5]])
-    assert(passivity.ispassive(sys))
-
-    B *= 0
-    C *= 0
-    assert(passivity.ispassive(sys))
-
-    A *= 0
-    assert(passivity.ispassive(sys))
+    assert(passivity.ispassive(sys)==expected)

From cf0eac302a71897424ba8eeffd6b591cfbe1cde0 Mon Sep 17 00:00:00 2001
From: mark-yeatman <mark.x.yeatman@gmail.com>
Date: Tue, 14 Jun 2022 11:35:13 -0400
Subject: [PATCH 16/20] Run autopep8.

---
 control/passivity.py            |  4 ++--
 control/tests/passivity_test.py | 19 +++++++++++--------
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/control/passivity.py b/control/passivity.py
index b2cf5a09e..60b081826 100644
--- a/control/passivity.py
+++ b/control/passivity.py
@@ -78,7 +78,7 @@ def make_LMI_matrix(P):
     # crunch feasibility solution
     cvx.solvers.options['show_progress'] = False
     sol = cvx.solvers.sdp(c,
-                        Gs=[cvx.matrix(coefficents)],
-                        hs=[cvx.matrix(constants)])
+                          Gs=[cvx.matrix(coefficents)],
+                          hs=[cvx.matrix(constants)])
 
     return (sol["x"] is not None)
diff --git a/control/tests/passivity_test.py b/control/tests/passivity_test.py
index d413f6fa5..681d2f527 100644
--- a/control/tests/passivity_test.py
+++ b/control/tests/passivity_test.py
@@ -25,20 +25,23 @@ def test_ispassive():
 
     assert(not passivity.ispassive(sys))
 
+
 A_d = numpy.array([[-2, 0], [0, 0]])
 A = numpy.array([[-3, 0], [0, -2]])
 B = numpy.array([[0], [1]])
 C = numpy.array([[-1, 2]])
 D = numpy.array([[1.5]])
+
+
 @cvxoptonly
 @pytest.mark.parametrize(
-    "test_input,expected", 
-    [((A,B,C,D*0.0), True), 
-     ((A_d,B,C,D), True), 
-     ((A*1e12,B,C,D*0), True), 
-     ((A,B*0,C*0,D), True),
-     ((A*0,B,C,D), True),
-     ((A*0,B*0,C*0,D*0), True)])
+    "test_input,expected",
+    [((A, B, C, D*0.0), True),
+     ((A_d, B, C, D), True),
+     ((A*1e12, B, C, D*0), True),
+     ((A, B*0, C*0, D), True),
+     ((A*0, B, C, D), True),
+     ((A*0, B*0, C*0, D*0), True)])
 def test_ispassive_edge_cases(test_input, expected):
 
     # strictly proper
@@ -47,4 +50,4 @@ def test_ispassive_edge_cases(test_input, expected):
     C = test_input[2]
     D = test_input[3]
     sys = ss(A, B, C, D)
-    assert(passivity.ispassive(sys)==expected)
+    assert(passivity.ispassive(sys) == expected)

From 7e47d8060c49dd89b52fc62e849da7c521a51119 Mon Sep 17 00:00:00 2001
From: mark-yeatman <mark.x.yeatman@gmail.com>
Date: Wed, 15 Jun 2022 21:22:54 -0400
Subject: [PATCH 17/20] Add wrapper like functionality for ispassive(), so that
 it can be called in an object oriented style as a LTI class member. Added
 unit tests for transfer function and oo style calls. Ran autopep8 on lti.py.

---
 control/lti.py                  | 18 +++++++++++++-----
 control/passivity.py            |  3 +++
 control/tests/passivity_test.py | 22 +++++++++++++++++++++-
 3 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/control/lti.py b/control/lti.py
index fdb4946cd..4f6624748 100644
--- a/control/lti.py
+++ b/control/lti.py
@@ -13,6 +13,7 @@
 """
 
 import numpy as np
+
 from numpy import absolute, real, angle, abs
 from warnings import warn
 from . import config
@@ -21,6 +22,7 @@
 __all__ = ['poles', 'zeros', 'damp', 'evalfr', 'frequency_response',
            'freqresp', 'dcgain', 'pole', 'zero']
 
+
 class LTI(NamedIOSystem):
     """LTI is a parent class to linear time-invariant (LTI) system objects.
 
@@ -44,6 +46,7 @@ class LTI(NamedIOSystem):
     Note: dt processing has been moved to the NamedIOSystem class.
 
     """
+
     def __init__(self, inputs=1, outputs=1, states=None, name=None, **kwargs):
         """Assign the LTI object's numbers of inputs and ouputs."""
         super().__init__(
@@ -71,8 +74,7 @@ def _set_inputs(self, value):
 
     #: Deprecated
     inputs = property(
-        _get_inputs, _set_inputs, doc=
-        """
+        _get_inputs, _set_inputs, doc="""
         Deprecated attribute; use :attr:`ninputs` instead.
 
         The ``inputs`` attribute was used to store the number of system
@@ -94,8 +96,7 @@ def _set_outputs(self, value):
 
     #: Deprecated
     outputs = property(
-        _get_outputs, _set_outputs, doc=
-        """
+        _get_outputs, _set_outputs, doc="""
         Deprecated attribute; use :attr:`noutputs` instead.
 
         The ``outputs`` attribute was used to store the number of system
@@ -201,6 +202,11 @@ def _dcgain(self, warn_infinite):
         else:
             return zeroresp
 
+    def ispassive(self):
+        # importing here prevents circular dependancy
+        from control.passivity import ispassive
+        ispassive(self)
+
     #
     # Deprecated functions
     #
@@ -321,7 +327,7 @@ def damp(sys, doprint=True):
     wn, damping, poles = sys.damp()
     if doprint:
         print('_____Eigenvalue______ Damping___ Frequency_')
-        for p, d, w in zip(poles, damping, wn) :
+        for p, d, w in zip(poles, damping, wn):
             if abs(p.imag) < 1e-12:
                 print("%10.4g            %10.4g %10.4g" %
                       (p.real, 1.0, -p.real))
@@ -330,6 +336,7 @@ def damp(sys, doprint=True):
                       (p.real, p.imag, d, w))
     return wn, damping, poles
 
+
 def evalfr(sys, x, squeeze=None):
     """Evaluate the transfer function of an LTI system for complex frequency x.
 
@@ -388,6 +395,7 @@ def evalfr(sys, x, squeeze=None):
     """
     return sys.__call__(x, squeeze=squeeze)
 
+
 def frequency_response(sys, omega, squeeze=None):
     """Frequency response of an LTI system at multiple angular frequencies.
 
diff --git a/control/passivity.py b/control/passivity.py
index 60b081826..e833fbf96 100644
--- a/control/passivity.py
+++ b/control/passivity.py
@@ -4,6 +4,7 @@
 '''
 
 import numpy as np
+from control import statesp as ss
 
 try:
     import cvxopt as cvx
@@ -35,6 +36,8 @@ def ispassive(sys):
     if cvx is None:
         raise ModuleNotFoundError("cvxopt required for passivity module")
 
+    sys = ss._convert_to_statespace(sys)
+
     A = sys.A
     B = sys.B
     C = sys.C
diff --git a/control/tests/passivity_test.py b/control/tests/passivity_test.py
index 681d2f527..09ef42b4a 100644
--- a/control/tests/passivity_test.py
+++ b/control/tests/passivity_test.py
@@ -4,7 +4,7 @@
 '''
 import pytest
 import numpy
-from control import ss, passivity
+from control import ss, passivity, tf
 from control.tests.conftest import cvxoptonly
 
 
@@ -51,3 +51,23 @@ def test_ispassive_edge_cases(test_input, expected):
     D = test_input[3]
     sys = ss(A, B, C, D)
     assert(passivity.ispassive(sys) == expected)
+
+
+def test_transfer_function():
+    sys = tf([1], [1, -2])
+    assert(passivity.ispassive(sys))
+
+    sys = tf([1], [1, 2])
+    assert(not passivity.ispassive(sys))
+
+
+def test_oo_style():
+    A = numpy.array([[0, 1], [-2, -2]])
+    B = numpy.array([[0], [1]])
+    C = numpy.array([[-1, 2]])
+    D = numpy.array([[1.5]])
+    sys = ss(A, B, C, D)
+    assert(sys.ispassive())
+
+    sys = tf([1], [1, -2])
+    assert(sys.ispassive())

From ce11d0be328af73179307d4b63071968175fd537 Mon Sep 17 00:00:00 2001
From: Ben Greiner <code@bnavigator.de>
Date: Thu, 16 Jun 2022 13:28:32 +0200
Subject: [PATCH 18/20] mark the whole passivity_test module as skippable

---
 control/tests/passivity_test.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/control/tests/passivity_test.py b/control/tests/passivity_test.py
index 09ef42b4a..2a12f10df 100644
--- a/control/tests/passivity_test.py
+++ b/control/tests/passivity_test.py
@@ -8,7 +8,9 @@
 from control.tests.conftest import cvxoptonly
 
 
-@cvxoptonly
+pytestmark = cvxoptonly
+
+
 def test_ispassive():
     A = numpy.array([[0, 1], [-2, -2]])
     B = numpy.array([[0], [1]])
@@ -33,7 +35,6 @@ def test_ispassive():
 D = numpy.array([[1.5]])
 
 
-@cvxoptonly
 @pytest.mark.parametrize(
     "test_input,expected",
     [((A, B, C, D*0.0), True),

From f7d74b2a52e4653d602512664f6ac00111f897c6 Mon Sep 17 00:00:00 2001
From: Mark <myeatman@oxefit.com>
Date: Thu, 16 Jun 2022 09:14:24 -0500
Subject: [PATCH 19/20] Fix bug in tests and lti.py.

---
 control/lti.py                  | 2 +-
 control/tests/passivity_test.py | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/control/lti.py b/control/lti.py
index 4f6624748..b87944cd0 100644
--- a/control/lti.py
+++ b/control/lti.py
@@ -205,7 +205,7 @@ def _dcgain(self, warn_infinite):
     def ispassive(self):
         # importing here prevents circular dependancy
         from control.passivity import ispassive
-        ispassive(self)
+        return ispassive(self)
 
     #
     # Deprecated functions
diff --git a/control/tests/passivity_test.py b/control/tests/passivity_test.py
index 2a12f10df..791d70b6c 100644
--- a/control/tests/passivity_test.py
+++ b/control/tests/passivity_test.py
@@ -55,10 +55,10 @@ def test_ispassive_edge_cases(test_input, expected):
 
 
 def test_transfer_function():
-    sys = tf([1], [1, -2])
+    sys = tf([1], [1, 2])
     assert(passivity.ispassive(sys))
 
-    sys = tf([1], [1, 2])
+    sys = tf([1], [1, -2])
     assert(not passivity.ispassive(sys))
 
 
@@ -70,5 +70,5 @@ def test_oo_style():
     sys = ss(A, B, C, D)
     assert(sys.ispassive())
 
-    sys = tf([1], [1, -2])
+    sys = tf([1], [1, 2])
     assert(sys.ispassive())

From c2255b0b087696e09717cc1591c1038b357f4ae7 Mon Sep 17 00:00:00 2001
From: Mark <myeatman@oxefit.com>
Date: Thu, 16 Jun 2022 09:45:50 -0500
Subject: [PATCH 20/20] Fix merge issue.

---
 control/tests/conftest.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/control/tests/conftest.py b/control/tests/conftest.py
index ac35748f3..1201b8746 100644
--- a/control/tests/conftest.py
+++ b/control/tests/conftest.py
@@ -17,6 +17,8 @@
 # pytest.param(marks=)
 slycotonly = pytest.mark.skipif(not control.exception.slycot_check(),
                                 reason="slycot not installed")
+cvxoptonly = pytest.mark.skipif(not control.exception.cvxopt_check(),
+                                reason="cvxopt not installed")
 matrixfilter = pytest.mark.filterwarnings("ignore:.*matrix subclass:"
                                           "PendingDeprecationWarning")
 matrixerrorfilter = pytest.mark.filterwarnings("error:.*matrix subclass:"