#10795: Fix and upgrade double dense matrix QR decomposition
-------------------------------+--------------------------------------------
    Reporter:  rbeezer         |         Owner:  jason, was  
        Type:  defect          |        Status:  needs_review
    Priority:  minor           |     Milestone:  sage-4.7.2  
   Component:  linear algebra  |    Resolution:              
    Keywords:  beginner        |   Work_issues:              
    Upstream:  N/A             |      Reviewer:  Martin Raum 
      Author:  Rob Beezer      |        Merged:              
Dependencies:                  |  
-------------------------------+--------------------------------------------
Changes (by jdemeyer):

  * status:  new => needs_review


Comment:

 It seems that this patch causes failures in a
 non-reproducible way.  Is there some randomness in the algorithm?
 For example, I just got this failure on sage.math.washington.edu (a
 machine on which I remember the test succeeding):
 {{{
 sage -t -long  -force_lib devel/sage/sage/matrix/matrix_double_dense.pyx
 **********************************************************************
 File
 
"/mnt/usb1/scratch/buildbot/sage/sage-1/sage_binary/build/sage-4.7.2.alpha2/devel
 /sage-main/sage/matrix/matrix_double_dense.pyx",
 line 1766:
     sage: Q
 Expected:
     [ -0.359210604054   0.569326179705   0.368048420509   0.641385845805]
     [  0.179605302027  -0.144590775798   0.925041158846  -0.301884576418]
     [  0.179605302027  -0.704880032016  0.0774617736597   0.681825307224]
     [  0.898026510134   0.397624633445 -0.0532812182975   0.180566192161]
 Got:
     [-0.359210604054  0.569326179705  0.616028985113  0.409076682956]
     [ 0.179605302027 -0.144590775798   0.69237507842 -0.683704756325]
     [ 0.179605302027 -0.704880032016  0.374205463771  0.575201135981]
     [ 0.898026510134  0.397624633445 0.0330954856071  0.185331397251]
 **********************************************************************
 File
 
"/mnt/usb1/scratch/buildbot/sage/sage-1/sage_binary/build/sage-4.7.2.alpha2/devel
 /sage-main/sage/matrix/matrix_double_dense.pyx",
 line 1771:
     sage: R
 Expected:
     [    -5.56776436283       2.6940795304      -2.6940795304]
     [                 0     -3.56958477752      3.56958477752]
     [                 0                  0 -9.93013661299e-16]
     [                 0                  0                  0]
 Got:
     [   -5.56776436283      2.6940795304     -2.6940795304]
     [                0    -3.56958477752     3.56958477752]
     [                0                 0 -4.4408920985e-16]
     [                0                 0                 0]
 **********************************************************************
 }}}

-- 
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10795#comment:6>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica, 
and MATLAB

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