Okay, I didn't realize that I changed the behavior of lambda in 1.3. to make it "scale-invariant", but it is worth discussing whether this is a good change. In 1.2, we multiply lambda by the number ratings in each sub-problem. This makes it "scale-invariant" for explicit feedback. However, in implicit feedback model, a user's sub-problem contains all item factors. Then the question is whether we should multiply lambda by the number of explicit ratings from this user or by the total number of items. We used the former in 1.2 but changed to the latter in 1.3. So you should try a smaller lambda to get a similar result in 1.3.
Sean and Shuo, which approach do you prefer? Do you know any existing work discussing this? Best, Xiangrui On Fri, Mar 27, 2015 at 11:27 AM, Xiangrui Meng <men...@gmail.com> wrote: > This sounds like a bug ... Did you try a different lambda? It would be > great if you can share your dataset or re-produce this issue on the > public dataset. Thanks! -Xiangrui > > On Thu, Mar 26, 2015 at 7:56 AM, Ravi Mody <rmody...@gmail.com> wrote: >> After upgrading to 1.3.0, ALS.trainImplicit() has been returning vastly >> smaller factors (and hence scores). For example, the first few product's >> factor values in 1.2.0 are (0.04821, -0.00674, -0.0325). In 1.3.0, the >> first few factor values are (2.535456E-8, 1.690301E-8, 6.99245E-8). This >> difference of several orders of magnitude is consistent throughout both user >> and product. The recommendations from 1.2.0 are subjectively much better >> than in 1.3.0. 1.3.0 trains significantly faster than 1.2.0, and uses less >> memory. >> >> My first thought is that there is too much regularization in the 1.3.0 >> results, but I'm using the same lambda parameter value. This is a snippet of >> my scala code: >> ..... >> val rank = 75 >> val numIterations = 15 >> val alpha = 10 >> val lambda = 0.01 >> val model = ALS.trainImplicit(train_data, rank, numIterations, >> lambda=lambda, alpha=alpha) >> ..... >> >> The code and input data are identical across both versions. Did anything >> change between the two versions I'm not aware of? I'd appreciate any help! >> --------------------------------------------------------------------- To unsubscribe, e-mail: user-unsubscr...@spark.apache.org For additional commands, e-mail: user-h...@spark.apache.org
