Use Barycentric Lagrange Interpolation for controls in Simulation #1056
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The state segment end values are no longer a variable in the birkhoff transcription. Birkhoff linear constraints are now improving sparsity on a lot of problems. Fixed an issue with abs/promoted path names for timeseries plotting.
…ile, simulation and solution cases do not match.
…but needs derivatives and polynomials to work also
… derivative matrices when n is not high enough.
… have no higher order derivatives
Added pre_announce to testflo main run.
…causing incorrect derivatives in the ODEIntegrationComp. The partials in the control interpolation and elsewhere seem correct, so I'm not sure whats happening there. In the meantime, I've reverted to Vandermonde interpolation for ExplicitShooting, except when doing pure simulation, in which case the more accurate Barycentric interpolant is used.
kaushikponnapalli
approved these changes
Mar 29, 2024
robfalck
changed the title
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Summary
Previously dymos had used Vandermonde interpolation for controls in ExplicitShooting, because matrices could be calculated apriori. However, the exponents on the terms in the Vandermonde matrix go up to N (the number of nodes of interpolation). When the number of nodes is large (greater than 20-30), this exceeds the floating point limitations and accuracy of the interpolation suffers.
Barycentric interpolation fixes this issue, though it is somewhat more expensive.
To improve performance, numba's just-in-time compilation is used to compute some derivatives (the control rates, derivatives of the rates). Numba is optional for this implementation, and it will work seemlessly (albeit more slowly) without it.
For pure simulation, users are unlikely to notice any performance difference at all until segments grow to ~50 nodes or so.
Related Issues
Backwards incompatibilities
None
New Dependencies
Numba jit is used to make a 4-nested for loop more performant. Numba is an optional dependency and