The Matrix Calculus You Need for Deep Learning
So I have a question somewhat related to this that I never knew where/who to ask (well actually I asked a few mathematicians at a university I work with whose answers I couldn't understand - their answers were almost as impenetrable as the Wikipedia page, and some engineering scientists who I thought would be more into 'applied math' but they didn't know. So I'm hoping some data science people reading this would better understand where I'm coming from, and be able to explain at my primitive math skills level).So, some time ago I contracted out writing some code for fitting a logistic regression onto a given set of observations. There were some specific requirements, but I think I should have been able to piece something myself together using mainstream LA libraries; some of them even hint at 'you could fit a logistic regression using these functions' but no complete examples. But I didn't understand well enough so I contracted it out.The woman who ended up writing the code used a 'Hessian' matrix to do so (she actually wrote two functions doing the same thing, one used this Hessian approach - I think the idea was that it would be faster but there wasn't a lot of time and it never got tweaked enough to make a difference).So my question - is there a layman's explanation for what a Hessian matrix is, and how it applies to fitting a logistic model? Also (with an eye to the future of my project), does it have applications for non-linear regressions?Alternatively, are there any books where this is covered? I have most standard stats/applied stats/operations research books, as well as a few like the no bullshit guide to linear algebra, but none cover this specific issue - or even how to fit a logistic regression at all, on a practical level (so not just 'conceptually you do xyz, implementation is left as an exercise for the reader').