IIRC the main reasons for deprecating Lanczos was that in contrast to SSVD, it does not use a constant number of MapReduce jobs and that our implementation has the constraint that all the resulting vectors have to fit into the memory of the driver machine.
Best, Sebastian On 01.08.2013 12:15, Fernando Fernández wrote: > Hi everyone, > > Sorry if I duplicate the question but I've been looking for an answer and I > haven't found an explanation other than it's not being used (together with > some other algorithms). If it's been discussed in depth before maybe you > can point me to some link with the discussion. > > I have successfully used Lanczos in several projects and it's been a > surprise to me finding that the main reason (according to what I've read > that might not be the full story) is that it's not being used. At the > begining I supposed it was because SSVD is supposed to be much faster with > similar results, but after making some tests I have found that running > times are similar or even worse than lanczos for some configurations (I > have tried several combinations of parameters, given child processes enough > memory, etc. and had no success in running SSVD at least in 3/4 of time > Lanczos runs, thouh they might be some combinations of parameters I have > still not tried). It seems to be quite tricky to find a good combination of > parameters for SSVD and I have seen also a precision loss in some examples > that makes me not confident in migrating Lanczos to SSVD from now on (How > far can I trust results from a combination of parameters that runs in > significant less time, or at least a good time?). > > Can someone convince me that SSVD is actually a better option than Lanczos? > (I'm totally willing to be convinced... :) ) > > Thank you very much in advance. > > Fernando. >
