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Re: nolinear regression model
Posted:
Jul 8, 2008 2:56 AM
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"Miroslav Balda" <balda.nospam@cdm.it.cas.cz> wrote in
message <g4uuhm$t79$1@fred.mathworks.com>...
:
SNIP
:
> Hi Ender
>
> Could you send me some of your data? I'll try to solve it.
>
> Mira
Hi
I decided to show you a solution on a simulated example.
Here is the code:
% Ender 2008-07-08
a = 10, b = -8, c = -.2 % Model parameters
t = (0:.1:1)'; % should be a column vector
f = a + b*(1-exp(t/c)) + .2*randn(size(t));
% Column vector of residuals
res = @(x) x(1) + x(2)*(1-exp(t/x(3))) - f;
% solve it with rather bad estimate of parameters
x0 = [5,3,-.1];
[x,ssq,cnt] = LMFnlsq(res,x0)
plot(t,f, t,res(x)+f,'r'), grid
The output from the run has been:
>> Ender
a =
10
b =
-8
c =
-0.2000
x =
10.0640
-7.9915
-0.1926
ssq =
0.2140
cnt =
8
You see that after 8 evaluations of function and Jacobin
matrix, the solution of the example is close to the initial
a, b, and c. Differences are caused by random deviations in
the formula for f.
Hope it helps.
Mira
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