Here we provide references to books and courses about data analysis in general, which might also be helpful in the context of Mahout.
General Background Materials
Don’t be overwhelmed by all the maths, you can do a lot in Mahout with some
basic knowledge. The books will help you understand your
data better, and ask better questions both of Mahout’s APIs, and also of
the Mahout community. And unlike learning some particular software tool,
these are skills that will remain useful decades later.
As a pre-requisite to probability and statistics, you’ll need basic calculus. A maths for scientists text might be useful here such as ‘Mathematics for Engineers and Scientists’, Alan Jeffrey, Chapman & Hall/CRC. (openlibrary)
For matrix computations/decomposition/factorization etc.:
Peter V. O’Neil Introduction to Linear Algebra, great book for beginners (with some knowledge in calculus). It is not comprehensive, but, it will be a good place to start and the author starts by explaining the concepts with regards to vector spaces which I found to be a more natural way of explaining.