step through Operon's implementation of NNLS with Ceres

[lacava]

since operon accomplishes this in a similar fashion, a good bet would be to

• install their code
• put breakpoints in the autodiff/ceres weight optimization portions
• step through the code and write a description of how they achieve this

see this file: https://github.com/heal-research/operon/blob/79d9f6cdd725c4724aa3f911de2bb08d65e3b20c/include/operon/nnls/nnls.hpp

• find an entry point from one of the tests that uses Ceres. (They also have Eigen's nls solver, avoid that)

[lacava]

update from meeting: post an issue on operon asking for documentation on how to build and run the tests.