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<div>Hello all,</div>
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<div>first of all, thanks a lot for your effort. I must say that I don't really have anyone to run to for asking about mathematical models - I could go to the mathematicians at the University, but I don't know anyone there and I barelly know where the institute is located...</div>
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<div>therefore I decided to insert my simplest table in here (it is actually very simple) - may be someone here knows which kind of mathematical model I could use?</div>
<div>I have been searching for it in literature, but I don't seem to be in the right path...</div>
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<div>So attached you will find my data table as well as the scilab commands I used to create the respective graph. I mean, my data is already interpolated...shouldn't it be easy to get a function (z,x,y) out of it?</div>
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<div>I would be very very thankful for any help...I'm getting a bit desperate...</div>
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<div>best regards,</div>
<div>Larissa</div>
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<div style="margin:0 0 10px 0;"><b>Gesendet:</b> Dienstag, 25. Juni 2013 um 11:09 Uhr<br/>
<b>Von:</b> "CRETE Denis" <denis.crete@thalesgroup.com><br/>
<b>An:</b> "International users mailing list for Scilab." <users@lists.scilab.org><br/>
<b>Betreff:</b> Re: [Scilab-users] Convert x, y, z data into a z=f(x,y) function</div>
<div name="quoted-content">Hello,<br/>
<br/>
The general procedure for fitting data in the case of 2 variables is the following:<br/>
// First define your mathematical model by changing the following line<br/>
deff('z=MyFunction(x,y)', 'z=p(1)*x + p(2)*y + p(3)*x.*y');<br/>
// Store all experimental data in a single array ExD; X, Y, Z assumed to be 1 x NZ vectors<br/>
ExD=[X;Y;Z];<br/>
// Define the error function (to be minimized with respect to the parameters p)<br/>
deff('erro=G(p,ExD)','x=ExD(1),y=ExD(2), z=ExD(3), erro=z-MyFunction(x,y)')<br/>
// Fit experimental data contained in W<br/>
// The column vector p0 is an initial guess of the values for the parameters of your Model<br/>
[p,err]=datafit(G,ExD,p0)<br/>
// you can check values generated with<br/>
MyFunction(X,Y)<br/>
<br/>
HTH<br/>
Denis<br/>
<br/>
-----Message d'origine-----<br/>
De : users-bounces@lists.scilab.org [mailto:users-bounces@lists.scilab.org] De la part de Dang, Christophe<br/>
Envoyé : mardi 25 juin 2013 10:20<br/>
À : International users mailing list for Scilab.<br/>
Objet : Re: [Scilab-users] Convert x, y, z data into a z=f(x,y) function<br/>
<br/>
Hello,<br/>
<br/>
De la part de Larissa<br/>
Envoyé : mardi 25 juin 2013 09:52<br/>
<br/>
> I conducted an experiment and thus my results are composed of x,y,z<br/>
> data,<br/>
[...]<br/>
> but I can't figure out how to get an equation "z=f(x,y)" out of it.<br/>
<br/>
This is more a math problem than a Scilab problem.<br/>
<br/>
You must have a mathematical model, i.e. a parametric formula, then you can adjust the parameters by regression (or maximum likehood).<br/>
<br/>
You may have theoretical models that derive from elementary assumptions<br/>
-- you usually find such model in the bibliography --, or use a "nice model that fit the global shape"<br/>
-- you may ask the math laboratory in your neighbourhood, this is usually polynomials, exponentials, statistical laws...<br/>
<br/>
So if you come to us with a parametric model, we will be able to help you.<br/>
<br/>
best regards.<br/>
<br/>
--<br/>
Christophe Dang Ngoc Chan<br/>
Mechanical calculation engineer<br/>
<br/>
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