Bt job. For details, see working notes in MAHOUT-376.
Uses hadoop deprecated API wherever new api has not been updated
(MAHOUT-593), hence @SuppressWarning("deprecation").
This job outputs either Bt in its standard output, or upper triangular
matrices representing BBt partial sums if that's requested . If the latter
mode is enabled, then we accumulate BBt outer product sums in upper
triangular accumulator and output it at the end of the job, thus saving space
and BBt job.
This job also outputs Q and Bt and optionally BBt. Bt is output to standard
job output (part-*) and Q and BBt use named multiple outputs.