Hi, Ted Thanks for your comment. The original matrix is:
qRef - 3 x 3 12.00000 -51.00000 4.00000 6.00000 167.00000 -68.00000 -4.00000 24.00000 -41.00000 The result of mahout: q - 3 x 3 -0.85714 0.39429 -0.33143 -0.42857 -0.90286 0.03429 0.28571 -0.17143 -0.94286 r - 3 x 3 -14.00000 -21.00000 14.00000 0.00000-175.00000 70.00000 0.00000 0.00000 35.00000 The result of wiki(http://en.wikipedia.org/wiki/QR_decomposition): q - 3 x 3 -0.85714 0.3110 -0.4106 -0.42857 -0.8728 0.2335 -0.28571 0.3761 0.8814 r - 3 x 3 -14.00000 -8.4286 -2.0000 0.00000 -187.1736 -35.1241 0.00000 0.00000 -32.1761 I notice that there are differences in computing householder vector, given input vector x, In mahout, householder vector is computed as v= x/||x||, however in wiki, it is computed as u = x+||x||*e1, v=u/||u||. So, would you please give me some clues about why did mahout(actually JAMA) do like that? Thanks for your reply! Liu Liu On Thu, Jan 19, 2012 at 8:01 AM, Ted Dunning <ted.dunn...@gmail.com> wrote: > There are lots of QR decomposition algorithms and the results are not > necessarily unique, especially for rank deficient inputs. > > If you post your exact results, I could comment more specifically. Without > more details, I really can't answer your question in any specific way. > > On Wed, Jan 18, 2012 at 9:39 AM, 刘鎏 <liuliu....@gmail.com> wrote: > > > Hi, > > When I run QRDecomposition in mahout , I find the result of Q or R is > > different from the example in wiki( > > > http://en.wikipedia.org/wiki/QR_decomposition#Using_Householder_reflections > > ). > > After reading the source code, I find the implement of QR decomposition > is > > exactly different from the tradition way such as the procedure in wiki. > > Could any one show why mahout implement it in such a way? Thanks for your > > replies! > > > > Liu Liu > > > -- 刘鎏 奇艺公司 北京市海淀区海淀东三街2号欧美汇大厦8层 100080 Phone: (010) 6267-7240 E-mail: liu...@qiyi.com MSN: alex_rose2...@hotmail.com
