Enable setting Δt in minimal_period

[JonasKoziorek]

Enables user to select keyword argumet Δt, eg. time step between points in po.points trajectory. This refers to comment in #22. If the keyword is not specified, Δt is set to default T/100. This keyword argument is only valid for continuous-time systems.

[codecov-commenter]

Welcome to Codecov 🎉

Once you merge this PR into your default branch, you're all set! Codecov will compare coverage reports and display results in all future pull requests.

Thanks for integrating Codecov - We've got you covered ☂️

[Datseris]

That was not really my comment. My comment was that minimal_period should not care about Dt. It should re-use the same points of the PO it took as input. The points on the PO remain the same if you have 5 times the period or 1. So my suggestion is that minimal_period should never call complete_orbit. Rather it should just remake the same periodic orbit with the same po.points and just the reduced period.

[JonasKoziorek]

The points on the PO remain the same if you have 5 times the period or 1.

The geometric curve in the state space remains (in theory) the same. In practice if we compute 50 * minimal_T trajectory and the PO is unstable, the ODE solver will diverge from the correct trajectory. Furthermore, N * minimal_T might have duplicate points compared to minimal_T.

[Datseris]

Okay. So, if I understand correctly, we, the codebase never call minimal_period. This is aconvenience function we offer to the user. Hence, it is fine if the orbit is re-completed. Correct?

[JonasKoziorek]

We don't call minimal_period by default anywhere. For now it is a convenience function for the user. In the future I think there might be a situation where minimal_period is called inside of a detection algorithm. Function minimal_period is not something that would be called in a loop or so, hence I think it's fine to recompute the orbit.