#4503: numerical noise in matrix_double_dense on intel mac os X 10.5: SVD
----------------------------+-----------------------------------------------
Reporter: jhpalmieri | Owner: somebody
Type: defect | Status: new
Priority: major | Milestone: sage-3.2
Component: linear algebra | Keywords: numerical noise, matrix
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(This has only been reported on intel macs running 10.4 or 10.5.)
From [http://groups.google.com/group/sage-
devel/browse_frm/thread/fae59a9a9a53b8c0 sage-devel]:
{{{
sage: m = matrix(RDF,3,2,range(6)); m
[0.0 1.0]
[2.0 3.0]
[4.0 5.0]
sage: U,S,V = m.SVD()
sage: U*S*V.transpose() # random low order bits
[0.0 1.0]
[2.0 3.0]
[4.0 5.0]
max((U*S*V.transpose()-m).list())
1.7763568394e-15
}}}
This leads to a doctest failure for {{{matrix_double_dense.py}}}.
Jason Grout suggests:
{{{
Okay, apparently the doctest just needs a looser bound; what you get is
still within reason for numerical issues. Currently we see if that
maximum is < 1e-15. Changing it to 1e-14 should fix this.
}}}
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/4503>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
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