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Possible bug: control.interconnect fails to construct a extended system with zero input and one output (D matrix shape mismatch) #1176
Description
About the problem
Summary
I attempted to simulate a control system with an output-feedback controller, defining a plant and a controller as subsystems.
When using control.interconnect to connect these subsystems, an error occurs because an extended system obtained by connecting subsystems has zero input and one output.
Is it impossible to define a system with zero input and one output using the control.interconnect function?
Error message
control.exception.ControlDimension: Incompatible dimensions of D matrix; expected (1, 0) but found (0, 0)
System information
- OS: macOS Sonoma 14.3.1
- Python: 3.12.2
- python-control: 0.10.2
Cause of this problem
When we set the inputs and outputs of the extended system as zero input and one input, the D matrix of the extended system has (1, 0) dimension.
However, the dimension of D matrix is converted to (0, 0) dimension by _ssmatrix function at line 218 of statesp.py.
As a result, the mismatch of the dimensions occurs.
(When we set both inputs and outputs to zero, the error does not occur.)
To reproduce the error
import numpy as np
import control as ct
def main():
# Define the coefficient matrices of plant P
A = np.array(
[
[1.00, 1.00],
[0.00, -2.0],
]
)
B = np.array(
[
[0.00],
[1.00]
]
)
C = np.array(
[
[1.00, 0.00]
]
)
# Define the coefficient matrices of controller C
A_c = np.array(
[
[2.25, 1.00],
[-5.0, -0.5]
]
)
B_c = np.array(
[
[-1.25],
[4.500]
]
)
C_c = np.array(
[
[-0.50, 1.500]
]
)
# Define the subsystems
P = ct.ss(
A,
B,
C,
np.zeros([C.shape[0], B.shape[1]]),
inputs=[f'u_p{i}' for i in range(B.shape[1])],
outputs=[f'y_p{i}' for i in range(C.shape[0])],
name='P',
dt=True
)
C = ct.ss(
A_c,
B_c,
C_c,
np.zeros([C_c.shape[0], B_c.shape[1]]),
inputs=[f'y_p{i}' for i in range(B_c.shape[1])],
outputs=[f'u_p{i}' for i in range(C_c.shape[0])],
name='C',
dt=True
)
sys = ct.interconnect(
[P, C],
inplist=None,
outlist=[f'y_p{i}' for i in range(P.C.shape[0])]
)
if __name__ == '__main__':
main()
Activity
murrayrm commentedon Jul 27, 2025
I took a quick look and the problem is not with
interconnect, but rather with the wayStateSpacesystems are initialized.For whoever picks this one up, there is some code in
_ssmatrix(used to preprocess state space matrices) that is converting the shape of theDmatrix incorrectly:What is happening is that the
Dmatrix for this example has shape (1, 0) [1 output, 0 inputs)] and it gets converted to shape (0, 0), causing an error. I think the fix is to also check thesizeof the array, so that[]and[[]]both get converted to an empty array (which is later cast to the correct shape inStateSpace.__init__).