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<DIV><SPAN class=328270209-01072013><FONT color=#0000ff size=2
face=Arial>Hi,</FONT></SPAN></DIV>
<DIV><SPAN class=328270209-01072013><FONT color=#0000ff size=2
face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=328270209-01072013><FONT color=#0000ff size=2 face=Arial>You
are asking a question which in general has no answer. There are an
infinite number of models which can fit your data. You need to find some
possible candidate model forms based on physical properties and then try fitting
to them. You are probably looking for a fit which leaves residues which
are Gaussian and mean zero (but that's not always true...).</FONT></SPAN></DIV>
<DIV><SPAN class=328270209-01072013><FONT color=#0000ff size=2
face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=328270209-01072013><FONT color=#0000ff size=2 face=Arial>Try
giving us a clue about where the data come from. Maybe somebody has the
physical background to suggest some models. If not, try plotting the data
and guessing a model from the shape. To me the shape looks vaguely
exponential or logarithmic, so maybe plotting as log-linear or log-log will give
a clue.</FONT></SPAN></DIV>
<DIV><SPAN class=328270209-01072013><FONT color=#0000ff size=2
face=Arial></FONT></SPAN> </DIV>
<DIV><SPAN class=328270209-01072013><FONT color=#0000ff size=2
face=Arial>HTH,</FONT></SPAN></DIV>
<DIV><SPAN class=328270209-01072013><FONT color=#0000ff size=2
face=Arial>Mike.</FONT></SPAN></DIV>
<DIV><SPAN class=328270209-01072013><FONT color=#0000ff size=2
face=Arial></FONT></SPAN> </DIV>
<BLOCKQUOTE style="MARGIN-RIGHT: 0px" dir=ltr>
<DIV dir=ltr class=OutlookMessageHeader align=left><FONT size=2
face=Tahoma>-----Original Message-----<BR><B>From:</B>
users-bounces@lists.scilab.org [mailto:users-bounces@lists.scilab.org]<B>On
Behalf Of </B>Larissa Schultze<BR><B>Sent:</B> 01 July 2013
09:43<BR><B>To:</B> International users mailing list for
Scilab.<BR><B>Subject:</B> Re: [Scilab-users] Convert x, y, z data into a
z=f(x,y) function<BR><BR></FONT></DIV>
<DIV style="FONT-FAMILY: Verdana; FONT-SIZE: 12px">
<DIV>
<DIV>Hello all,</DIV>
<DIV> </DIV>
<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>
<DIV> </DIV>
<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>
<DIV> </DIV>
<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>
<DIV> </DIV>
<DIV>I would be very very thankful for any help...I'm getting a bit
desperate...</DIV>
<DIV> </DIV>
<DIV>best regards,</DIV>
<DIV>Larissa</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>
<DIV
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name="quote">
<DIV style="MARGIN: 0px 0px 10px"><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>______________________________________________________________________<BR><BR>This
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