[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: matrix determinant calculation
From: |
A Scotte Hodel |
Subject: |
Re: matrix determinant calculation |
Date: |
Thu, 26 May 2005 12:13:23 -0500 |
Others have explained why the computed result is reasonable.
If you're interested in further details on numerical roundoff and the
associated problems, I recommend "Matrix Computations" by Golub and Van
Loan. It's an excellent text and reference. I strongly recommend it.
When testing for singularity on a computer, it's better to use the
singular value decomposition (developed by Prof Golub in the 50's) than
a determinant calculation. The ratio of largest singular value over
the smallest singular value is called the two-norm condition of a
matrix, and is a good measure of how hard it is to accurately invert a
matrix on a computer. Being *close* to singular is just as bad as
*being* singular, on a computer.
I hope this is useful to you.
On May 26, 2005, at 12:49 AM, Hui Zhang wrote:
hi, i am not sure the following problem is already reported or not.
It happens both version 2.1.50 (sparc-sun-solaris2.8) and
version 2.1.57 (i686-pc-linux-gnu).
octave:1> a=[1,2,3;4,5,6;7,8,9]
a =
1 2 3
4 5 6
7 8 9
octave:2> det(a)
ans = 6.6613e-16
THE ANS is WRONG.
Best regards,
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Hui Zhang Ph.D. Candidate & Research Assistant
VLSI System Design Lab
Department of Electrical and Computer Engineering
State University of New York at Stony Brook
Stony Brook, NY 11794-2350
Tel: 631-632-1068 Email: address@hidden
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-------------------------------------------------------------
Octave is freely available under the terms of the GNU GPL.
Octave's home on the web: http://www.octave.org
How to fund new projects: http://www.octave.org/funding.html
Subscription information: http://www.octave.org/archive.html
-------------------------------------------------------------
- Re: matrix determinant calculation,
A Scotte Hodel <=