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RobotLocomotion / drake

Model-based design and verification for robotics.
https://drake.mit.edu
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Need a non-symbolic way to report if a System is time-invariant #10914

Open sherm1 opened 5 years ago

sherm1 commented 5 years ago

(Requested by @RussTedrake)

Currently SystemSymbolicInspector can be used to determine whether a System is time-invariant, provided (a) the system can be transmogrified to symbolic, and (b) you have time to wait for the answer. For other cases it would be useful to have a System::IsTimeInvariant() method analogous to the existing System::HasDirectFeedthrough() method, which can be overridden in cases where the System designer can simply provide the answer.

Russ, if you can explain the intended application a little that would be helpful. I'm guessing this is low priority at the moment -- please raise it if it becomes urgent.

RussTedrake commented 5 years ago

That's a perfect explanation, thanks.

The use case is that we have many algorithms that assume time-invariance.. they should be checking for it. Here are a few examples I found quickly: https://github.com/RobotLocomotion/drake/blob/master/systems/controllers/dynamic_programming.h#L62 https://github.com/RobotLocomotion/drake/blob/master/systems/analysis/lyapunov.h#L27 and there are more on the way.

(I suspect even the trajectory optimization code assumes it). Probably even Linearize. We haven't had it, and so have been sloppy about this.

sherm1 commented 4 years ago

See also discussion in #12253 and #12709.