ValueError("Time steps T must match sampling time" #332
Description
Got this error when using timeresp.py. Checked the source code, I think the problem is at line 337-338:
if dt < sys.dt:
raise ValueError("Time steps T must match sampling time")
It will be better to use the following, since float rounding error can be smaller or larger:
if abs(dt-sys.dt) > 1e-5:
Activity
murrayrm commentedon Jul 23, 2019
Can you attach a code snippet that generates the error? This check is done in the discrete time portion of the code and so a small error between
dtandsys.dtshould not really occur (the only allowed differences betweendtandsys.dtshould be specifying a simulation sample time that is an integer multiple of the system sampling time).Also, can you indicate which version of
python-controlyou are using (control.__version__will tell you). The line that you indicated doesn't seem to match the latest release.bj2sn commentedon Jul 24, 2019
My "control" version is 0.8.2, Python version 3.7.3 (IPython 7.6.1) Windows 10 (64 bits)
The problem can be demonstrated by a simple test:
import numpy as np
samp_rate = 500e3
T = np.arange(100)
T[1]-T[0]
Out[5]: 2e-06
T[2]-T[1]
Out[6]: 2e-06
T[3]-T[2]
Out[7]: 2.0000000000000003e-06
T[4]-T[3]
Out[8]: 1.9999999999999995e-06
So, if we call timeresp.py with T[3:] as our time steps in simulation, line 265 "dt = T[1] - T[0]" will yield dt = 1.9999999999999995e-06, but sys.dt should be 2e-6. Subsequently, line 337 will raise the ValueError.
If simulation time uses T, or T[1:], or T[2:] will have no problem!
bj2sn commentedon Jul 24, 2019
It seems the problem goes away by changing line 337 in timeresp.py to:
if abs(dt - sys.dt) > 1e-18:
murrayrm commentedon Jul 24, 2019
Thanks for the extra info @bj2sn. A fix will be a bit more complicated because the discrete time simulation routines allow you to specify a sample time for the simulation that is a multiple of the sampling time for the system. So, for example, you can have that
dtis2 * sys.dt. On the current master, this check is done on line 362.Will put this on my list of things to fix.
fix discete time simulation time step issue python-control#332
fix discete time simulation time step issue #332 (#356)
murrayrm commentedon Jan 2, 2020
Fixed in PR #356.