After I found an insanely huge and existential bug in my code, Price-Whelan (Princeton) and I did a full code review of my project that takes advantage of chemical-abundance invariance to determine dynamical invariants. The big issue is that the action computation is expensive; it involves some kind of integration or quadrature. As we were discussing this, Eugene Vasiliev (Cambridge) joined us and suggested ways to speed up the action calculation using the energy invariant to aid in the integration.
[Insert tire screeching noise] We don't need actions! We only need some kind of invariant for this project. Indeed, I have tried various different invariants and they all work equally well. So we can use the energy invariant, which requires no integration! Woah, and thanks Vasiliev! That sped up the code by factors of many hundreds, which we then partially compensated down by doing more complete MCMC samplings. But development cycle is far improved.
I also had a great planning session with Bonaca (Harvard) where we worked out coordinate systems and methods for making far more realistic our project to model the GD-1 stream gaps. We are modeling one of the gaps and spurs with a dark-matter (or really dense-object) interaction. We needed to make things far more realistic, because we want to rule out disk-passage events as gap causes. That requires that we have GD-1 orbiting in a Galaxy with a disk and the observer (us) in the right places at the right times. Things are complicated, because everything happens on the kinematic equivalent of the past light cone—the past star cone?
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