The documentation of his library (SnOB) is great: http://www.gatsby.ucl.ac.uk/~risi/SnOB/SnOB/SnOB.pdf
introductory slides on representation theory in machine learning: http://www.gatsby.ucl.ac.uk/~risi/courses/mini08/symmetric.p...
Full mini course: http://www.gatsby.ucl.ac.uk/~risi/courses/mini08/mini08.html