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RE: solving equation system
From: |
Hall, Benjamin |
Subject: |
RE: solving equation system |
Date: |
Tue, 19 Apr 2005 14:05:51 -0400 |
It looks like you're trying to fit a 4th-order polynomial to the data
xx = [124.5; 111; 88.9; 75.5; 63 ];
yy = [ 29.3; 126.7; 236.4; 284.7; 315.5];
which you can do using polyfit
coeffs = polyfit( xx, yy, 4 )
coeffs =
-1.0222e-05
3.5786e-03
-5.0372e-01
2.9366e+01
-2.6907e+02
-----Original Message-----
From: Madhusudan Singh [mailto:address@hidden
Sent: Tuesday, April 19, 2005 1:52 PM
To: address@hidden
Cc: address@hidden
Subject: Re: solving equation system
Looks simple. Define a coefficient matrix and solve it :
octave:6>
a=[1,124.5,124.5^2,124.5^3,124.5^4;1,111,111^2,111^3,111^4;1,88.9,88.9^2,88.
9^3,88.9^4;1,75.5,75.5^2,75.5^3,75.5^4;1,63,63^2,63^3,63^4]
a =
1.0000e+00 1.2450e+02 1.5500e+04 1.9298e+06 2.4026e+08
1.0000e+00 1.1100e+02 1.2321e+04 1.3676e+06 1.5181e+08
1.0000e+00 8.8900e+01 7.9032e+03 7.0260e+05 6.2461e+07
1.0000e+00 7.5500e+01 5.7002e+03 4.3037e+05 3.2493e+07
1.0000e+00 6.3000e+01 3.9690e+03 2.5005e+05 1.5753e+07
octave:7> f=[29.3,126.7,236.4,284.7,315.5]'
f =
29.300
126.700
236.400
284.700
315.500
octave:8> a\f
ans =
-2.6907e+02
2.9366e+01
-5.0372e-01
3.5786e-03
-1.0222e-05
I hope that someone can point out a shorter way to define the coefficient
matrix since all its rows are of the form [1,x,x^2,x^3,x^4].
HTH
On Tuesday 19 April 2005 12:15, Brigitte Diekhaus wrote:
> hello,
>
> it`s my first time using octave and I want to solve the following equation
> system:
>
> 29.3 = A*124.5^4+B*124.5^3+C*124.5^2+124.5*D+F,
> 126.7 = A*111^4+B*111^3+C*111^2+D*111+F,
> 236.4 = A*88.9^4+B*88.9^3+C*88.9^2+D*88.9+F,
> 284.7 = A*75.5^4+B*75.5^3+C*75.5^2+D*75.5+F,
> 315.5 = A*63^4+B*63^3+C*63^2+D*63+F },
>
> I need to find the variables {A,B,C,D,F}
>
> to get a function like this:
>
> y(x)=a*x^4+b*x^3+c*x^2+d*x+e
>
> I Don`t know the syntax I have to use with octave to solve this equation
> system.
>
> many thanks in advance.
>
> Brigitte
>
>
>
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Octave is freely available under the terms of the GNU GPL.
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Subscription information: http://www.octave.org/archive.html
-------------------------------------------------------------
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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
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