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Understanding how octave works...
From: |
Joerg Frochte |
Subject: |
Understanding how octave works... |
Date: |
Mon, 26 Jan 2004 15:14:15 +0100 |
User-agent: |
Mutt/1.4.1i |
Hello,
I often use octave to control results of a program that uses lapack.
I have got to solve the following :
A=[
0.00e+00 1.00e-01 0.00e+00 5.00e-03 0.00e+00 0.00e+00 0.00e+00
0.00e+00 1.67e-04 ;
0.00e+00 -1.00e-01 0.00e+00 5.00e-03 -0.00e+00 0.00e+00 -0.00e+00
0.00e+00 -1.67e-04 ;
-7.09e-02 4.48e-02 2.51e-03 1.01e-03 -3.18e-03 -5.94e-05 1.13e-04
-7.13e-05 1.50e-05 ;
-7.09e-02 -5.52e-02 2.51e-03 1.52e-03 3.91e-03 -5.94e-05 -1.39e-04
-1.08e-04 -2.80e-05 ;
-3.55e-02 7.24e-02 6.29e-04 2.62e-03 -2.57e-03 -7.43e-06 4.55e-05
-9.30e-05 6.33e-05 ;
0.00e+00 5.00e-02 0.00e+00 1.25e-03 0.00e+00 0.00e+00 0.00e+00
0.00e+00 2.08e-05 ;
-3.55e-02 -7.76e-02 6.29e-04 3.01e-03 2.75e-03 -7.43e-06 -4.88e-05
-1.07e-04 -7.78e-05 ;
0.00e+00 -5.00e-02 0.00e+00 1.25e-03 -0.00e+00 0.00e+00 -0.00e+00
0.00e+00 -2.08e-05 ;
-3.55e-02 -2.76e-02 6.29e-04 3.80e-04 9.78e-04 -7.43e-06 -1.73e-05
-1.35e-05 -3.50e-06 ;
-3.55e-02 2.24e-02 6.29e-04 2.51e-04 -7.95e-04 -7.43e-06 1.41e-05
-8.91e-06 1.88e-06 ;
-7.09e-02 -5.16e-03 2.51e-03 1.33e-05 3.66e-04 -5.94e-05 -1.30e-05
-9.44e-07 -2.29e-08 ;
]
b=[ 0.00e+00 0.00e+00 7.29e-02 8.51e-02 3.46e-02 0.00e+00 4.39e-02 0.00e+00
4.10e-02 3.80e-02 7.92e-02 ]
octave:16> A\b'
ans =
-1.1090e+00
3.7483e-04
-1.6496e-02
-4.5344e-04
1.7691e+00
1.0526e-03
8.8226e-01
2.5739e+00
-2.6411e-01
The result in octave is quite OK, but the result my own program computes
is very unpleasing.
ans = [ -7.12e+11-3.70e-05-6.03e+13 1.82e-03 1.74e+00-1.70e+15 1.48e-01
2.79e+00 6.10e-02 ]
This has something to do with the fact that A is very close to be singular.
octave:21> cond(A)
ans = 2.9251e+18
Nevertheless, the result of octave is more pleasing.
How does octave deal with such a situation?
I have the source-code but I am unable to find a point to start my analysis,
because I do not know how octave is designed.
Could you tell me how octave works in this situation or give me a file and
line where to start in the octave code?
Thanks very much,
Joerg Frochte
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- Understanding how octave works...,
Joerg Frochte <=