diff --git a/control/statesp.py b/control/statesp.py
index 6b3a1dff3..f04bc55b3 100644
--- a/control/statesp.py
+++ b/control/statesp.py
@@ -851,7 +851,7 @@ def slycot_laub(self, x):
# transformed state matrices, at, bt, ct.
# Start at the second frequency, already have the first.
- for kk, x_kk in enumerate(x_arr[1:len(x_arr)]):
+ for kk, x_kk in enumerate(x_arr[1:]):
result = tb05ad(n, m, p, x_kk, at, bt, ct, job='NH')
# When job='NH', result = (g_i, hinvb, info)
@@ -885,15 +885,29 @@ def horner(self, x, warn_infinite=True):
Attempts to use Laub's method from Slycot library, with a
fall-back to python code.
"""
+ # Make sure the argument is a 1D array of complex numbers
+ x_arr = np.atleast_1d(x).astype(complex, copy=False)
+
+ # return fast on systems with 0 or 1 state
+ if not config.defaults['statesp.use_numpy_matrix']:
+ if self.nstates == 0:
+ return self.D[:, :, np.newaxis] \
+ * np.ones_like(x_arr, dtype=complex)
+ if self.nstates == 1:
+ with np.errstate(divide='ignore', invalid='ignore'):
+ out = self.C[:, :, np.newaxis] \
+ / (x_arr - self.A[0, 0]) \
+ * self.B[:, :, np.newaxis] \
+ + self.D[:, :, np.newaxis]
+ out[np.isnan(out)] = complex(np.inf, np.nan)
+ return out
+
try:
- out = self.slycot_laub(x)
+ out = self.slycot_laub(x_arr)
except (ImportError, Exception):
# Fall back because either Slycot unavailable or cannot handle
# certain cases.
- # Make sure the argument is a 1D array of complex numbers
- x_arr = np.atleast_1d(x).astype(complex, copy=False)
-
# Make sure that we are operating on a simple list
if len(x_arr.shape) > 1:
raise ValueError("input list must be 1D")
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