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Test norm methods slycot and scipy separately #1201

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8d20519
test norm methods
bnavigator Feb 1, 2026
a7a98a0
mark slycot needing tests
bnavigator Feb 1, 2026
e3bfe9d
test some invalid parameters
bnavigator Feb 1, 2026
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2 changes: 1 addition & 1 deletion control/sysnorm.py
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Original file line number Diff line number Diff line change
Expand Up @@ -28,7 +28,7 @@ def _h2norm_slycot(sys, print_warning=True):
try:
from slycot import ab13bd
except ImportError:
ct.ControlSlycot("Can't find slycot module ab13bd")
raise ct.ControlSlycot("Can't find slycot module ab13bd")

try:
from slycot.exceptions import SlycotArithmeticError
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64 changes: 44 additions & 20 deletions control/tests/sysnorm_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -11,50 +11,54 @@
import pytest


def test_norm_1st_order_stable_system():
@pytest.mark.parametrize("method", [pytest.param("slycot", marks=pytest.mark.slycot), "scipy", None])
def test_norm_1st_order_stable_system(method):
"""First-order stable continuous-time system"""
s = ct.tf('s')

G1 = 1/(s+1)
assert np.allclose(ct.norm(G1, p='inf'), 1.0) # Comparison to norm computed in MATLAB
assert np.allclose(ct.norm(G1, p=2), 0.707106781186547) # Comparison to norm computed in MATLAB
assert np.allclose(ct.norm(G1, p='inf', method=method), 1.0) # Comparison to norm computed in MATLAB
assert np.allclose(ct.norm(G1, p=2, method=method), 0.707106781186547) # Comparison to norm computed in MATLAB

Gd1 = ct.sample_system(G1, 0.1)
assert np.allclose(ct.norm(Gd1, p='inf'), 1.0) # Comparison to norm computed in MATLAB
assert np.allclose(ct.norm(Gd1, p=2), 0.223513699524858) # Comparison to norm computed in MATLAB
assert np.allclose(ct.norm(Gd1, p='inf', method=method), 1.0) # Comparison to norm computed in MATLAB
assert np.allclose(ct.norm(Gd1, p=2, method=method), 0.223513699524858) # Comparison to norm computed in MATLAB


def test_norm_1st_order_unstable_system():
@pytest.mark.parametrize("method", [pytest.param("slycot", marks=pytest.mark.slycot), "scipy", None])
def test_norm_1st_order_unstable_system(method):
"""First-order unstable continuous-time system"""
s = ct.tf('s')

G2 = 1/(1-s)
assert np.allclose(ct.norm(G2, p='inf'), 1.0) # Comparison to norm computed in MATLAB
assert np.allclose(ct.norm(G2, p='inf', method=method), 1.0) # Comparison to norm computed in MATLAB
with pytest.warns(UserWarning, match="System is unstable!"):
assert ct.norm(G2, p=2) == float('inf') # Comparison to norm computed in MATLAB
assert ct.norm(G2, p=2, method=method) == float('inf') # Comparison to norm computed in MATLAB

Gd2 = ct.sample_system(G2, 0.1)
assert np.allclose(ct.norm(Gd2, p='inf'), 1.0) # Comparison to norm computed in MATLAB
assert np.allclose(ct.norm(Gd2, p='inf', method=method), 1.0) # Comparison to norm computed in MATLAB
with pytest.warns(UserWarning, match="System is unstable!"):
assert ct.norm(Gd2, p=2) == float('inf') # Comparison to norm computed in MATLAB
assert ct.norm(Gd2, p=2, method=method) == float('inf') # Comparison to norm computed in MATLAB

def test_norm_2nd_order_system_imag_poles():
@pytest.mark.parametrize("method", [pytest.param("slycot", marks=pytest.mark.slycot), "scipy", None])
def test_norm_2nd_order_system_imag_poles(method):
"""Second-order continuous-time system with poles on imaginary axis"""
s = ct.tf('s')

G3 = 1/(s**2+1)
with pytest.warns(UserWarning, match="Poles close to, or on, the imaginary axis."):
assert ct.norm(G3, p='inf') == float('inf') # Comparison to norm computed in MATLAB
assert ct.norm(G3, p='inf', method=method) == float('inf') # Comparison to norm computed in MATLAB
with pytest.warns(UserWarning, match="Poles close to, or on, the imaginary axis."):
assert ct.norm(G3, p=2) == float('inf') # Comparison to norm computed in MATLAB
assert ct.norm(G3, p=2, method=method) == float('inf') # Comparison to norm computed in MATLAB

Gd3 = ct.sample_system(G3, 0.1)
with pytest.warns(UserWarning, match="Poles close to, or on, the complex unit circle."):
assert ct.norm(Gd3, p='inf') == float('inf') # Comparison to norm computed in MATLAB
assert ct.norm(Gd3, p='inf', method=method) == float('inf') # Comparison to norm computed in MATLAB
with pytest.warns(UserWarning, match="Poles close to, or on, the complex unit circle."):
assert ct.norm(Gd3, p=2) == float('inf') # Comparison to norm computed in MATLAB
assert ct.norm(Gd3, p=2, method=method) == float('inf') # Comparison to norm computed in MATLAB

def test_norm_3rd_order_mimo_system():
@pytest.mark.parametrize("method", [pytest.param("slycot", marks=pytest.mark.slycot), "scipy", None])
def test_norm_3rd_order_mimo_system(method):
"""Third-order stable MIMO continuous-time system"""
A = np.array([[-1.017041847539126, -0.224182952826418, 0.042538079149249],
[-0.310374015319095, -0.516461581407780, -0.119195790221750],
Expand All @@ -66,9 +70,29 @@ def test_norm_3rd_order_mimo_system():
[-0.863652821988714, -1.214117043615409, -0.006849328103348]])
D = np.zeros((2,2))
G4 = ct.ss(A,B,C,D) # Random system generated in MATLAB
assert np.allclose(ct.norm(G4, p='inf'), 4.276759162964244) # Comparison to norm computed in MATLAB
assert np.allclose(ct.norm(G4, p=2), 2.237461821810309) # Comparison to norm computed in MATLAB
assert np.allclose(ct.norm(G4, p='inf', method=method), 4.276759162964244) # Comparison to norm computed in MATLAB
assert np.allclose(ct.norm(G4, p=2, method=method), 2.237461821810309) # Comparison to norm computed in MATLAB

Gd4 = ct.sample_system(G4, 0.1)
assert np.allclose(ct.norm(Gd4, p='inf'), 4.276759162964228) # Comparison to norm computed in MATLAB
assert np.allclose(ct.norm(Gd4, p=2), 0.707434962289554) # Comparison to norm computed in MATLAB
assert np.allclose(ct.norm(Gd4, p='inf', method=method), 4.276759162964228) # Comparison to norm computed in MATLAB
assert np.allclose(ct.norm(Gd4, p=2, method=method), 0.707434962289554) # Comparison to norm computed in MATLAB


@pytest.mark.noslycot
def test_sysnorm_no_slycot():
"""Test that sysnorm raises ControlSlycot when slycot is requested but not available"""
s = ct.tf('s')
G = 1/(s+1)

with pytest.raises(ct.ControlSlycot, match="Can't find slycot module ab13bd"):
ct.norm(G, p=2, method='slycot')


def test_norm_invalid_p():
"""Test that norm raises Error for invalid norm request"""
s = ct.tf('s')
G = 1/(s+1)

with pytest.raises(ct.ControlArgument,
match="Norm computation for p=myownnorm currently not supported."):
ct.norm(G, p='myownnorm', method=None)
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