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https://issues.apache.org/jira/browse/MAHOUT-797?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13167396#comment-13167396
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Dmitriy Lyubimov commented on MAHOUT-797:
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Thank you.
rank deficiency of the input, yes, that's what i thought. but i can't figure
how it may end up being singular, given that i generated it randomly. random
input is virtually guaranteed to be non-singular. Ok must be something with my
test program.
I guess i am also a little bit confused about this whole positive definite
thing. Y'Y is guaranteed to be Hermitian but is it guaranteed to be positive
definite? At least in my experiments Y'Y doesn't seem to ever end up positive
definite.
> MapReduce SSVD: provide alternative B-pipeline per B=R' ^{-1} Y'A
> -----------------------------------------------------------------
>
> Key: MAHOUT-797
> URL: https://issues.apache.org/jira/browse/MAHOUT-797
> Project: Mahout
> Issue Type: Improvement
> Affects Versions: 0.5, 0.6
> Reporter: Dmitriy Lyubimov
> Assignee: Dmitriy Lyubimov
> Fix For: Backlog
>
> Attachments: MAHOUT-797.pdf
>
> Original Estimate: 48h
> Remaining Estimate: 48h
>
> Since alternative flow using Cholesky decomposition is extremely easy to add
> to existing computations of BB', I am thinking of just adding an option that
> chooses between B-pipeline with QR step and B-pipeline with Y'Y-Cholesky
> step.
> Ongoing work and some initial code (Y'Y step) is here
> https://github.com/dlyubimov/mahout-commits/tree/MAHOUT-797.
> I also want to fix what's left unfixed in MAHOUT-638.
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