I spent a chunk of the day with Melissa Ness (MPIA), fitting empirical models to APOGEE infrared spectra of stars. The idea is to do a simple linear supervised classification or regression, in which we figure out the dependence of the spectra on key stellar parameters, using a "training set" of stars with good stellar parameters. We worked in the pair-coding mode. By the end of the day we could show that we are able to identify regions of the spectrum that might serve as good metallicity indicators, relatively insensitive to temperature and log-g. The hopes for this project range from empirical metallicity index identification to label de-noising to building a full data-driven (supervised) stellar parameter pipeline. We ended our coding day pretty optimistic.