After reading this thread: http://mail-archives.apache.org/mod_mbox/mahout-user/201102.mbox/%3caanlktinq5k4xrm7nabwn8qobxzgvobbot2rtjzsv4...@mail.gmail.com%3E
Wiki-SVD: M = U S V* (* = transposed) The output of Mahout-SVD is (U S) right? So... How do I get V from (U S) and M? Is V = M (U S)* (because this is, what the calculation in the example is)? Thanks Stefan 2011/6/6 Stefan Wienert <ste...@wienert.cc>: > https://cwiki.apache.org/confluence/display/MAHOUT/Dimensional+Reduction > > What is done: > > Input: > tf-idf-matrix (docs x terms) 6076937 x 20444 > > "SVD" of tf-idf-matrix (rank 100) produces the eigenvector (and > eigenvalues) of tf-idf-matrix, called: > svd (concepts x terms) 87 x 20444 > > transpose tf-idf-matrix: > tf-idf-matrix-transpose (terms x docs) 20444 x 6076937 > > transpose svd: > svd-transpose (terms x concepts) 20444 x 87 > > matrix multiply: > tf-idf-matrix-transpose x svd-transpose = result > (terms x docs) x (terms x concepts) = (docs x concepts) > > so... I do understand, that the "svd" here is not SVD from wikipedia. > It only does the Lanczos algorithm and some magic which produces the >> Instead either the left or right (but usually the right) eigenvectors >> premultiplied by the diagonal or the square root of the >> diagonal element. > from > http://mail-archives.apache.org/mod_mbox/mahout-user/201102.mbox/%3CAANLkTi=rta7tfrm8zi60vcfya5xf+dbfrj8pcds2n...@mail.gmail.com%3E > > so my question: what is the output of the SVD in mahout. And what do I > have to calculate to get the "right singular value" from svd? > > Thanks, > Stefan > > 2011/6/6 Stefan Wienert <ste...@wienert.cc>: >> https://cwiki.apache.org/confluence/display/MAHOUT/Dimensional+Reduction >> >> the last step is the matrix multiplication: >> --arg --numRowsA --arg 20444 \ >> --arg --numColsA --arg 6076937 \ >> --arg --numRowsB --arg 20444 \ >> --arg --numColsB --arg 87 \ >> so the result is a 6,076,937 x 87 matrix >> >> the input has 6,076,937 (each with 20,444 terms). so the result of >> matrix multiplication has to be the right singular value regarding to >> the dimensions. >> >> so the result is the "concept-document vector matrix" (as I think, >> these is also called "document vectors" ?) >> >> 2011/6/6 Ted Dunning <ted.dunn...@gmail.com>: >>> Yes. These are term vectors, not document vectors. >>> >>> There is an additional step that can be run to produce document vectors. >>> >>> On Sun, Jun 5, 2011 at 1:16 PM, Stefan Wienert <ste...@wienert.cc> wrote: >>> >>>> compared to SVD, is the result is the "right singular value"? >>>> >>> >> >> >> >> -- >> Stefan Wienert >> >> http://www.wienert.cc >> ste...@wienert.cc >> >> Telefon: +495251-2026838 >> Mobil: +49176-40170270 >> > > > > -- > Stefan Wienert > > http://www.wienert.cc > ste...@wienert.cc > > Telefon: +495251-2026838 > Mobil: +49176-40170270 > -- Stefan Wienert http://www.wienert.cc ste...@wienert.cc Telefon: +495251-2026838 Mobil: +49176-40170270
