empirical yields; galaxy alignments; linear algebra foo.

Early in the day, Kathryn Johnston (Columbia) convened the local Local Group group (yes, I wrote that right) at Columbia. We had presentations from various directions (and I could only be at half of the day). Subjective highlights for me included the following: Andrew Emerick (Columbia) showed that there is a strong prediction that in dwarf galaxies, AGB-star yields will be differently distributed than supernovae yields. That should be observable, and might be an important input to my life-long goal of deriving nucleosynthetic yields from the data (rather than theory). Wyn Evans (Cambridge) showed that you can measure some statistics of the alignments of dwarf satellite galaxies with respect to their primary-galaxy hosts, using the comparison of the Milky Way and M31. M31 is more constraining, because we aren't sitting near the center of it! These alignments appear to have the right sign (but maybe the wrong amplitude?) to match theoretical predictions.

Late in the day, Christina Eilers (MPIA) showed up and we discussed with Dan Foreman-Mackey (Flatiron) our code issues. He noted that we are doing the same linear-algebra operations (or very similar ones) over and over again. We should not use solve, but rather use cho_factor and then cho_solve that permits fast operation given the pre-existing factorization. He also pointed out that in the places where we have missing data, the factorization can be updated in a fast way rather than fully re-computed. Those are good ideas! As I often like to say, many of my super-powers boil down to just knowing who to ask about linear algebra.

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