occultations, determinants

In our semi-weekly arXiv coffee, Fed Bianco (NYU) showed us some papers about Pluto, including an occultation study (Pluto occults a background star) and the implications for Pluto's atmosphere. But then we got onto occultations and she showed us some amazing Kuiper-Belt-object occultation data she has from fast cameras on Hawaii. The coolest thing (to me) is that the occulters are so tiny, the occultations look different from different observatories, even Haleakala to Mauna Kea! Tycho Brahe would have loved that: The effect could have been used to prove (pretty much) the heliocentric model.

I spent a good chunk of the afternoon at the brand-new Simons Center for Data Analysis with applied mathematicians Leslie Greengard (Simons, NYU) and Mike O'Neil (NYU), talking about big matrices and inverting them and getting their determinants. Their codes are super-good at inverting (or, equivalently, providing operators that multiply by the inverse), even the ten-million by ten-million matrices I am going to need to invert, but not necessarily at computing determinants. We discussed and then left it as a homework problem. The context was cosmology, but this problem comes up everywhere that Gaussian Processes are being used.