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? 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. thanks Yang
