On Tue, Sep 10, 2013 at 5:48 PM, Yang <[email protected]> wrote: > in the simple equation describing SVD: > > A = USV > > I guess the original matrix A has to have every value filled, so that > mathematics will be able to carry out the calculation, right?
No. A may be sparse, where 0 elements are omitted. But, logically, every element has a value, yes. > > but the mahout package described here: > https://cwiki.apache.org/confluence/display/MAHOUT/Dimensional+Reduction > > https://cwiki.apache.org/confluence/display/MAHOUT/SVD+-+Singular+Value+Decomposition > > > allows for input to be sparse, so most elements of A are missing values. so > I wonder how mahout takes care of the missing values? this paper: > http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA439541 > fills missing values with some sort of averages, which sounds rather > arbitrary. in strict SVD, "missing" values are always 0s. I put "missing" into quotes because they are not really missing, this is just a way compress input. > > > thanks > Yang
