Looks to be a multivariate calculus text by the Hubbards:
It covers in detail many topics often glossed over while keeping an eye on what is actually applicable, including such things as (taken from their page):
> More big matrices! We included the Perron-Frobenius theorem, and its application to Google's PageRank algorithm More singular values! We included a detailed proof of the singular value decomposition, and show how it applies to facial recognition: "how does Facebook apply names to pictures?"