moving things to the right of the bar

At lunch I gave the Flatiron CCA a taste of the science going on with Gaia DR2 in a short lunch talk. And before that I prepared my slides. All that counts as research by my rules.

My research highlight of the day, however, was a conversation with Neige Frankel (MPIA) about her probabilistic model for radial migration in the Milky Way disk. She doesn't have a good quantitative model for the selection function for her data, so she doesn't want her model to generate the three-space positions of the stars in her sample. At the same time, the structural parameters of the Milky Way disk are important. So she wants a model for the stellar properties, conditioned on the stellar positions. There are two ways to do this. The first is to write a graphical model where arrows only come from (and never go to) the stellar positions. We did that, but Frankel doesn't like that option, because the model only has simple analytic form when the arrows go to the positions.

The other option is to use the factorization formula p(a, b) = p(a|b) p(b). The stellar positions can be moved from the left side of the vertical bar to the right side by dividing by a pdf for the positions. We wrote that down, drew the relevant graphical models, and discussed changes to her text. She has beautiful results, TBA.

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