Dymos 1.6.0

Release Notes for Dymos 1.6.0

October 17, 2022

Version 1.6.0 of Dymos implements many improvements since our last release.

The new AnalyticPhase is useful for when the state values are analytically known as functions of time and other parameters.
States are not only outputs and therefore values cannot be fixed or bounded, though they can be constrained with boundary and path constraints.
AnalyticPhase does not support controls (or polynomial controls).
Unlike other phase types which use the ODE solver in scipy.solve_ivp to propagate a trajectory based on the current control history, AnalyticPhase simply provides its outputs.
AnalyticPhase does not have a notion of segments.
Instead, it simply evaluates the value of the states at some set of N nodes, where N is given by the user and the node locations are the Legendre-Gauss-Lobatto nodes in non-dimensional phase time.

It will also be the last version of the code before we introduce more tailored phase classes that are more closely coupled to their transcription.
In the following 1.7.0 release, instantiating Phase will result in a deprecation warning and inform the user on how to change their phase instantiation calls.

Dymos now automatically generates a linkage report html file when appropriate.
This report looks similar to the N2, and helps to visualize the continuity of variables across phases within a trajectory.

Other changes include a significant cleanup of the timeseries output code, allowing users to rename states/controls/etc. in the timeseries outputs as they see fit.
Timeseries can now also provide approximate rates of outputs (based on fitting them on the current grid and interpolating the derivative of the resulting polynomial).
In an upcoming release, the user will be able to easily apply constraints to these approximated rates.

Backwards Incompatible API Changes & Deprecations

• State option connected_initial is deprecated in favor of input_initial. This is more in-line with the time option, and reflects the fact that there's no requirement that the user actually connect to the value.
• The Lagrange interpolation and differentiation matrices are now generated much more efficiently, but change in the order of operations may result in small numerical differences in interpolatation of states and controls (generally on the order of 1E-12).

Enhancements

• Refactored TimeComp to avoid unnecessary recalculation of partials. #759
• Added a new N2-like linkage report to show continuity of variables between phases. #764
• Added timeseries rates for pseudospectral transcriptions. #781
• Trajectory.phases subgroup is now available before setup. #782
• Changed time series plots directory to be under the problem reports directory. #784
• run_problem argument restart now allows a specific Case to be provided. #801
• Added warning when restarting with fix_final=True. #804
• Added the classic cart-pole example problem - thank you @kanekosh! #808
• Updated assert_timeseries_near_equal to work with more general cases #810
• Refactored the timeseries handling to be more general and less transcription-specific. #816
• Added AnalyticPhase for phases in which no numerical integration is necessary. #833

Bug Fixes

• Fixed an error when an invalid rate source is provided for a state. #761
• Fixed a bug in size of trajectory parameters as passed to phases. #770
• Minor changes to fix occasional report testing failures. #785
• Fixed example code impacted by matplotlib change #826
• Fixed condition under which trajectory linkage reports are generated. #828
• Fixed issue in reentry example that was causing optimization to fail under SLSQP. #831

Miscellaneous

• Updated optimizer settings to improve convergence of the racecar example. #752
• Changed setup to use setuptools instead of distutils. #757
• Changes to use OpenMDAOs updated report system. #763
• Updated github workflow and setup.py. #768
• Switched to using mamba in CI workflow due to issues with conda. #772
• Updated optimizer settings to improve convergence of two-burn orbit raise example. #775
• Cleaned up error message from assert_cases_equal test utility a bit. #779
• Cleaned up CI and testing. #788
• Fixed two problems with the linkage report test #793
• Updated pyoptsparse build in github workflows #805
• Added small changes to improve coverage. #809
• Fixed CI dependency issues based on some broken jupyter-book dependencies. #812
• Various code cleanup items added. #807
• Made a few minor cleanups for the cartpole example. #815