[mathgenius]

I suspect the real answer to your question is "in your own head, and with your own pen and paper." Amazingly, you cannot learn mathematics from reading books. Especially the abstract stuff. It is just too opaque. Not until you start to manipulate the symbols yourself, in your own way, does it start to make sense. Having said that, I would still like to recommend a book to read :-) This is big-boy maths (i am not shitting you), explained with cartoons and a bazillion examples from things like sensor networks, robotics, pattern recognition, electromagnetism, it goes on and on. Just published, but also available for free. I bought several copies. It blows my mind that a mathematician took the time to explain these advanced topics to the mere mortals:

"Elemantary Applied Topology", Robert Ghrist. http://www.math.upenn.edu/~ghrist/notes.html

Although you probably need to have some idea of multi-variate calculus (and linear algebra) before you get started.