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Add the ability to split an input to an interconnected system #1049
Description
Discussed in #1047
Originally posted by corbinklett October 9, 2024
If I have an input that is external to an interconnected system, and I want this external input to connect into multiple systems contained within, the only way I can think to do this is by using set_input_map. Is there a more elegant way? Even when I use set_input_map, I still get the "unused input" warning.
Part of the motivation for this question is that it is difficult to understand how an external input is being used if you can only specify it in terms of the subsystem that it connects to. It might be intended for the input to connect to multiple subsystems.
Here is an example of how I have implemented:
import numpy as np
import control as ct
def dynamics(t, x, u, p):
A = np.array([[0, 1], [-p['spring_constant'], -p['damping_coefficient']]])
B = np.array([[0], [1]])
return A @ x + B @ u
def outputs(t, x, u, p):
C = np.array([[1, 0]])
D = np.array([[0]])
return C @ x + D @ u
sys1 = ct.nlsys(updfcn=dynamics, outfcn=outputs, states=['pos', 'vel'], inputs=['u1'], outputs=['pos'], name='sys1')
sys1.params = {'spring_constant': 10, 'damping_coefficient': 0.5}
sys2 = ct.nlsys(updfcn=dynamics, outfcn=outputs, states=['pos', 'vel'], inputs=['u2'], outputs=['pos'], name='sys2')
sys2.params = {'spring_constant': 1, 'damping_coefficient': 1}
sys = ct.interconnect(
(sys1, sys2),
# inplist=['u'], # only works if both subsystem inputs are named u
outlist=['sys1.pos', 'sys2.pos'],
outputs=['pos1', 'pos2']
)
# /venv/lib/python3.12/site-packages/control/nlsys.py:1192: UserWarning: Unused input(s) in InterconnectedSystem: (1, 0)=sys2.u2; (0, 0)=sys1.u1
sys.set_input_map(np.array([[1],[1]]))
sys.set_inputs('external_input')
t = np.linspace(0, 10, 1000)
u0 = lambda t: 1
U = np.array([
[u0(ti) for ti in t]
])
results = ct.input_output_response(sys, T=t, U=U)
p = results.plot()
p.figure.show()
```</div>
Activity
murrayrm commentedon Oct 12, 2024
It shouldn't be too hard to implement this functionality, and I agree it is natural to create systems in the way you described above (without having to resort to manual construction via
set_input_map).murrayrm commentedon Nov 23, 2024
I've looked into this a bit further and implementing the functionality above would require a fairly significant change to the current code. As noted in #1047, this functionality can be implemented using the following syntax: