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[Octave-bug-tracker] [bug #33503] null.m: tolerance for zero in basis el
From: |
Olaf Till |
Subject: |
[Octave-bug-tracker] [bug #33503] null.m: tolerance for zero in basis elements |
Date: |
Thu, 09 Jun 2011 17:03:27 +0000 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.16) Gecko/20110429 Iceweasel/3.5.16 (like Firefox/3.5.16) |
URL:
<http://savannah.gnu.org/bugs/?33503>
Summary: null.m: tolerance for zero in basis elements
Project: GNU Octave
Submitted by: i7tiol
Submitted on: Thu 09 Jun 2011 05:03:26 PM GMT
Category: None
Severity: 3 - Normal
Priority: 5 - Normal
Item Group: Incorrect Result
Status: None
Assigned to: None
Originator Name: Olaf Till
Originator Email:
Open/Closed: Open
Discussion Lock: Any
Release: dev
Operating System: GNU/Linux
_______________________________________________________
Details:
Octave version: 3.5.0+, stable branch, release 5bf8af73fc34 (2011-06-01)
Short description: tolerance for setting basis elements to zero possibly too
high.
Long description: Unfortunately I can't theoretically derive a suitable value
for this tolerance. But I had a practical problem in which for theoretical
reasons a certain element of the basis of the null-space of some matrix should
be zero. Due to very slight differences in this matrix (accuracy of
calculation) between two systems with Octave, the said element was returned by
null() as zero on one system and not as zero on the other system (same null()
version, in particular same tolerance used: eps). A larger tolerance "tol" is
used by null() for assuming elements of S (from svd()) to be zero. If this
tolerance "tol" were also used for setting elements of the returned basis to
zero, I would get the expected result of zero on both systems (the order of
magnitude of "tol" would be just enough for that).
So I suggest that null() should use the calculated tolerance "tol" also for
setting basis elements to zero.
_______________________________________________________
Reply to this item at:
<http://savannah.gnu.org/bugs/?33503>
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- [Octave-bug-tracker] [bug #33503] null.m: tolerance for zero in basis elements,
Olaf Till <=
- [Octave-bug-tracker] [bug #33503] null.m: tolerance for zero in basis elements, Jordi Gutiérrez Hermoso, 2011/06/09
- [Octave-bug-tracker] [bug #33503] null.m: tolerance for zero in basis elements, Olaf Till, 2011/06/09
- [Octave-bug-tracker] [bug #33503] null.m: tolerance for zero in basis elements, Jordi Gutiérrez Hermoso, 2011/06/09
- [Octave-bug-tracker] [bug #33503] null.m: tolerance for zero in basis elements, Olaf Till, 2011/06/09
- [Octave-bug-tracker] [bug #33503] null.m: tolerance for zero in basis elements, Olaf Till, 2011/06/10
- [Octave-bug-tracker] [bug #33503] null.m: tolerance for zero in basis elements, Jordi Gutiérrez Hermoso, 2011/06/10
- [Octave-bug-tracker] [bug #33503] null.m: tolerance for zero in basis elements, Olaf Till, 2011/06/13
- [Octave-bug-tracker] [bug #33503] null.m: tolerance for zero in basis elements, Olaf Till, 2011/06/13
- [Octave-bug-tracker] [bug #33503] null.m: tolerance for zero in basis elements, Olaf Till, 2011/06/14
- [Octave-bug-tracker] [bug #33503] null.m: tolerance for zero in basis elements, Olaf Till, 2011/06/14