diff --git a/control/iosys.py b/control/iosys.py
index 19f527c22..9eb136cfb 100644
--- a/control/iosys.py
+++ b/control/iosys.py
@@ -114,12 +114,12 @@ class for a set of subclasses that are used to implement specific
The :class:`~control.InputOuputSystem` class (and its subclasses) makes
use of two special methods for implementing much of the work of the class:
- * _rhs(t, x, u): compute the right hand side of the differential or
- difference equation for the system. This must be specified by the
+ * _rhs(t, x, u, params={}): compute the right hand side of the differential
+ or difference equation for the system. This must be specified by the
subclass for the system.
- * _out(t, x, u): compute the output for the current state of the system.
- The default is to return the entire system state.
+ * _out(t, x, u, params={}): compute the output for the current state of the
+ system. The default is to return the entire system state.
"""
@@ -149,6 +149,7 @@ def __init__(self, params={}, **kwargs):
# default parameters
self.params = params.copy()
+ self._current_params = self.params.copy()
def __mul__(sys2, sys1):
"""Multiply two input/output systems (series interconnection)"""
@@ -369,7 +370,7 @@ def _rhs(self, t, x, u, params={}):
NotImplemented("Evaluation not implemented for system of type ",
type(self))
- def dynamics(self, t, x, u):
+ def dynamics(self, t, x, u, params={}):
"""Compute the dynamics of a differential or difference equation.
Given time `t`, input `u` and state `x`, returns the value of the
@@ -395,12 +396,15 @@ def dynamics(self, t, x, u):
current state
u : array_like
input
+ params : dict (optional)
+ system parameters
+
Returns
-------
dx/dt or x[t+dt] : ndarray
"""
- return self._rhs(t, x, u)
+ return self._rhs(t, x, u, params=params)
def _out(self, t, x, u, params={}):
"""Evaluate the output of a system at a given state, input, and time
@@ -414,7 +418,7 @@ def _out(self, t, x, u, params={}):
# If no output function was defined in subclass, return state
return x
- def output(self, t, x, u):
+ def output(self, t, x, u, params={}):
"""Compute the output of the system
Given time `t`, input `u` and state `x`, returns the output of the
@@ -432,12 +436,14 @@ def output(self, t, x, u):
current state
u : array_like
input
+ params : dict (optional)
+ system parameters
Returns
-------
y : ndarray
"""
- return self._out(t, x, u)
+ return self._out(t, x, u, params=params)
def feedback(self, other=1, sign=-1, params={}):
"""Feedback interconnection between two input/output systems
@@ -673,17 +679,9 @@ def _update_params(self, params={}, warning=True):
if params and warning:
warn("Parameters passed to LinearIOSystems are ignored.")
- def _rhs(self, t, x, u):
- # Convert input to column vector and then change output to 1D array
- xdot = self.A @ np.reshape(x, (-1, 1)) \
- + self.B @ np.reshape(u, (-1, 1))
- return np.array(xdot).reshape((-1,))
-
- def _out(self, t, x, u):
- # Convert input to column vector and then change output to 1D array
- y = self.C @ np.reshape(x, (-1, 1)) \
- + self.D @ np.reshape(u, (-1, 1))
- return np.array(y).reshape((-1,))
+ # inherit methods as necessary
+ _rhs = StateSpace._rhs
+ _out = StateSpace._out
def __repr__(self):
# Need to define so that I/O system gets used instead of StateSpace
@@ -799,7 +797,7 @@ def __str__(self):
f"Output: {self.outfcn}"
# Return the value of a static nonlinear system
- def __call__(sys, u, params=None, squeeze=None):
+ def __call__(sys, u, params={}, squeeze=None):
"""Evaluate a (static) nonlinearity at a given input value
If a nonlinear I/O system has no internal state, then evaluating the
@@ -825,12 +823,8 @@ def __call__(sys, u, params=None, squeeze=None):
"function evaluation is only supported for static "
"input/output systems")
- # If we received any parameters, update them before calling _out()
- if params is not None:
- sys._update_params(params)
-
# Evaluate the function on the argument
- out = sys._out(0, np.array((0,)), np.asarray(u))
+ out = sys._out(0, np.array((0,)), np.asarray(u), params)
_, out = _process_time_response(
None, out, issiso=sys.issiso(), squeeze=squeeze)
return out
@@ -840,13 +834,17 @@ def _update_params(self, params, warning=False):
self._current_params = self.params.copy()
self._current_params.update(params)
- def _rhs(self, t, x, u):
- xdot = self.updfcn(t, x, u, self._current_params) \
+ def _rhs(self, t, x, u, params={}):
+ current_params = self._current_params.copy()
+ current_params.update(params)
+ xdot = self.updfcn(t, x, u, current_params) \
if self.updfcn is not None else []
return np.array(xdot).reshape((-1,))
- def _out(self, t, x, u):
- y = self.outfcn(t, x, u, self._current_params) \
+ def _out(self, t, x, u, params={}):
+ current_params = self._current_params.copy()
+ current_params.update(params)
+ y = self.outfcn(t, x, u, current_params) \
if self.outfcn is not None else x
return np.array(y).reshape((-1,))
@@ -1018,7 +1016,7 @@ def _update_params(self, params, warning=False):
local.update(params) # update with locally passed parameters
sys._update_params(local, warning=warning)
- def _rhs(self, t, x, u):
+ def _rhs(self, t, x, u, params={}):
# Make sure state and input are vectors
x = np.array(x, ndmin=1)
u = np.array(u, ndmin=1)
@@ -1031,10 +1029,12 @@ def _rhs(self, t, x, u):
state_index, input_index = 0, 0 # Start at the beginning
for sys in self.syslist:
# Update the right hand side for this subsystem
+ sys_params = sys._current_params.copy()
+ sys_params.update(params)
if sys.nstates != 0:
xdot[state_index:state_index + sys.nstates] = sys._rhs(
t, x[state_index:state_index + sys.nstates],
- ulist[input_index:input_index + sys.ninputs])
+ ulist[input_index:input_index + sys.ninputs], sys_params)
# Update the state and input index counters
state_index += sys.nstates
@@ -1042,7 +1042,7 @@ def _rhs(self, t, x, u):
return xdot
- def _out(self, t, x, u):
+ def _out(self, t, x, u, params={}):
# Make sure state and input are vectors
x = np.array(x, ndmin=1)
u = np.array(u, ndmin=1)
@@ -2838,7 +2838,7 @@ def interconnect(syslist, connections=None, inplist=[], outlist=[], params={},
newsys.check_unused_signals(ignore_inputs, ignore_outputs)
# If all subsystems are linear systems, maintain linear structure
- if all([isinstance(sys, LinearIOSystem) for sys in syslist]):
+ if all([isinstance(sys, (LinearIOSystem, StateSpace)) for sys in syslist]):
return LinearICSystem(newsys, None)
return newsys
diff --git a/control/statesp.py b/control/statesp.py
index 374b036ca..b39bd90a0 100644
--- a/control/statesp.py
+++ b/control/statesp.py
@@ -346,9 +346,8 @@ def __init__(self, *args, init_namedio=True, **kwargs):
defaults = args[0] if len(args) == 1 else \
{'inputs': D.shape[1], 'outputs': D.shape[0],
'states': A.shape[0]}
- static = (A.size == 0)
name, inputs, outputs, states, dt = _process_namedio_keywords(
- kwargs, defaults, static=static, end=True)
+ kwargs, defaults, static=self._isstatic(), end=True)
# Initialize LTI (NamedIOSystem) object
super().__init__(
@@ -386,6 +385,9 @@ def __init__(self, *args, init_namedio=True, **kwargs):
# Check for states that don't do anything, and remove them
if remove_useless_states:
self._remove_useless_states()
+ # params for compatibility with LinearIOSystems
+ self.params = {}
+ self._current_params = self.params.copy()
#
# Class attributes
@@ -1388,8 +1390,22 @@ def dcgain(self, warn_infinite=False):
scalar is returned.
"""
return self._dcgain(warn_infinite)
+
+ def _rhs(self, t, x, u=None, params={}):
+ """Compute the right hand side of the differential or difference
+ equation for the system. Please :meth:`dynamics` for a more user-
+ friendly interface. """
- def dynamics(self, t, x, u=None):
+ x = np.reshape(x, (-1, 1)) # force to a column in case matrix
+ if u is None: # received t and x, but ignore t
+ output = self.A @ x
+ else: # received t, x, and u, ignore t
+ u = np.reshape(u, (-1, 1)) # force to column in case matrix
+ output = self.A @ x + self.B @ u
+
+ return output.reshape((-1,)) # return as row vector
+
+ def dynamics(self, t, x, u=None, params={}):
"""Compute the dynamics of the system
Given input `u` and state `x`, returns the dynamics of the state-space
@@ -1417,25 +1433,35 @@ def dynamics(self, t, x, u=None):
current state
u : array_like (optional)
input, zero if omitted
+ params : dict (optional)
+ included for compatibility but ignored for :class:`StateSpace` systems
Returns
-------
dx/dt or x[t+dt] : ndarray
"""
- x = np.reshape(x, (-1, 1)) # force to a column in case matrix
+ # chechs
if np.size(x) != self.nstates:
raise ValueError("len(x) must be equal to number of states")
+ if u is not None:
+ if np.size(u) != self.ninputs:
+ raise ValueError("len(u) must be equal to number of inputs")
+ return self._rhs(t, x, u, params)
+
+ def _out(self, t, x, u=None, params={}):
+ """Compute the output of the system system. Please :meth:`dynamics`
+ for a more user-friendly interface. """
+
+ x = np.reshape(x, (-1, 1)) # force to a column in case matrix
if u is None:
- return (self.A @ x).reshape((-1,)) # return as row vector
+ y = self.C @ x
else: # received t, x, and u, ignore t
- u = np.reshape(u, (-1, 1)) # force to column in case matrix
- if np.size(u) != self.ninputs:
- raise ValueError("len(u) must be equal to number of inputs")
- return (self.A @ x).reshape((-1,)) \
- + (self.B @ u).reshape((-1,)) # return as row vector
+ u = np.reshape(u, (-1, 1)) # force to a column in case matrix
+ y = self.C @ x + self.D @ u
+ return y.reshape((-1,)) # return as row vector
- def output(self, t, x, u=None):
+ def output(self, t, x, u=None, params={}):
"""Compute the output of the system
Given input `u` and state `x`, returns the output `y` of the
@@ -1465,19 +1491,19 @@ def output(self, t, x, u=None):
-------
y : ndarray
"""
- x = np.reshape(x, (-1, 1)) # force to a column in case matrix
if np.size(x) != self.nstates:
raise ValueError("len(x) must be equal to number of states")
-
- if u is None:
- return (self.C @ x).reshape((-1,)) # return as row vector
- else: # received t, x, and u, ignore t
- u = np.reshape(u, (-1, 1)) # force to a column in case matrix
+ if u is not None:
if np.size(u) != self.ninputs:
raise ValueError("len(u) must be equal to number of inputs")
- return (self.C @ x).reshape((-1,)) \
- + (self.D @ u).reshape((-1,)) # return as row vector
-
+ return self._out(t, x, u, params)
+
+ def _update_params(self, params={}, warning=False):
+ # Parameters not supported; issue a warning
+ if params and warning:
+ warn("Parameters passed to StateSpace system are ignored.")
+
+
def _isstatic(self):
"""True if and only if the system has no dynamics, that is,
if A and B are zero. """
diff --git a/control/tests/iosys_test.py b/control/tests/iosys_test.py
index 693be979e..cb38205a1 100644
--- a/control/tests/iosys_test.py
+++ b/control/tests/iosys_test.py
@@ -41,6 +41,9 @@ class TSys:
[[-1, 1], [0, -2]], [[0, 1], [1, 0]],
[[1, 0], [0, 1]], np.zeros((2, 2)))
+ # Create a static gain linear system
+ T.staticgain = ct.StateSpace(0, 0, 0, 1)
+
# Create simulation parameters
T.T = np.linspace(0, 10, 100)
T.U = np.sin(T.T)
@@ -66,6 +69,16 @@ def test_linear_iosys(self, tsys):
np.testing.assert_array_almost_equal(lti_t, ios_t)
np.testing.assert_allclose(lti_y, ios_y, atol=0.002, rtol=0.)
+ # Make sure that a combination of a LinearIOSystem and a StateSpace
+ # system results in a LinearIOSystem
+ assert isinstance(linsys*iosys, ios.LinearIOSystem)
+
+ # Make sure that a static linear system has dt=None
+ # and otherwise dt is as specified
+ assert ios.LinearIOSystem(tsys.staticgain).dt is None
+ assert ios.LinearIOSystem(tsys.staticgain, dt=.1).dt == .1
+
+
def test_tf2io(self, tsys):
# Create a transfer function from the state space system
linsys = tsys.siso_linsys
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