[RogerL]

Thanks for the offer. However, I kind of don't want to do things in Javascript, as Python is a fantastic platform for numeric computation, and so staying in that ecosystem makes a lot of sense (people can take my matplotlib code and go off and do their own plots for their filters, for example).

But I'm sort of at an inflection point. Is my book about using Python to do Kalman filtering, or is it about Kalman filtering, and it happens to use Python. So far it has largely been the latter, so I could see doing a Javascript version. But I think that puts my needs over the needs of the reader, which is probably wrong.