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Newbie question solving lin sys
From: |
John B. Thoo |
Subject: |
Newbie question solving lin sys |
Date: |
Fri, 27 Dec 2002 13:40:50 -0800 |
Hi. I'm very new to using Octave. I have two questions: 1. What am I
doing wrong in the following? 2. How can I do it more elegantly?
I want to solve the system Ax = T where A is the 12x12 Vandermonde
matrix
[ 1 0 0 ... 0 ]
[ 1 1 1 ... 1 ]
A = [ 1 2 2^2 ... 2^11 ]
[ ... ]
[ 1 11 11^2 ... 11^11 ]
T = [ 22 28 31 39 46 53 56 55 49 42 33 27 ]'
To do this, I enter in Octave:
octave:51> A = fliplr(vander([0,1,2,3,4,5,6,7,8,9,10,11]));
octave:52> T = [22;28;31;39;46;53;56;55;49;42;33;27];
octave:53> A\T
ans =
2.2000e+01
1.2932e+02
-3.3001e+02
3.5674e+02
-2.1174e+02
7.7512e+01
-1.8446e+01
2.9092e+00
-3.0191e-01
1.9818e-02
-7.4570e-04
1.2250e-05
*But* when I go to check my answers, they seem to be off. To check my
answers, I enter in Octave:
octave:54> s = 0;
octave:55> 22 + 129.32*s - 330.01*s**2 + 356.74*s**3 - 211.74*s**4 +
77.512*s**5 - 18.446*s**6 + 2.9092*s**7 - 0.30191*s**8 + 0.019818*s**9 -
0.0007457*s**10 + 0.00001225*s**11
ans = 22
octave:56> s = 1;
octave:57> 22 + 129.32*s - 330.01*s**2 + 356.74*s**3 - 211.74*s**4 +
77.512*s**5 - 18.446*s**6 + 2.9092*s**7 - 0.30191*s**8 + 0.019818*s**9 -
0.0007457*s**10 + 0.00001225*s**11
ans = 28.002
octave:58> s = 3;
and so on. The answers match well for the first few, but then they
drift. To summarize, I get
s | answers from Octave | supposed to be (T)
---------------------------------------------------
0 | 22 | 22
1 | 28.002 | 28
2 | 31.017 | 31
3 | 38.996 | 39
4 | 45.498 | 46
5 | 50.205 | 53
6 | 46.456 | 56
7 | 30.029 | 55
8 | - 5.5781 | 49
9 | -62.227 | 42
10 | -145.80 | 33
11 | -245.29 | 27
TIA for your help.
---John.
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-------------------------------------------------------------
- Newbie question solving lin sys,
John B. Thoo <=