Initial shot at SVD++.
Relies on the RatingsSGDFactorizer class introduced in
One could also think about several enhancements, e.g. having separate regularization constants for user and item factors.
I am also the author of the SVDPlusPlus class in MyMediaLite, so if there are any similarities, no need to worry – I am okay with relicensing this to the Apache 2.0 license.