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From: "John D'Errico" <woodchips@rochester.rr.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: griddata: can we get equation of surface?
Date: Mon, 4 Feb 2008 13:06:04 +0000 (UTC)
Organization: John D'Errico (1-3LEW5R)
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"murthy m" <mmurthy007@googlemail.com> wrote in message 
<fo6uau$47e$1@fred.mathworks.com>...
> "John D'Errico" <woodchips@rochester.rr.com> wrote in
> message <fo6rir$254$1@fred.mathworks.com>...
> 
> Thank you. Your 'gridfit' function is excellent. In my case,
> just to give you an idea of what I am trying, I have x,y and
> z matrices as given below and I want to choose an
> exponential function of the form
> Z(x,y)=exp[-(x-x(i))-(y-y(i))/m*m] where m is a constant to
> be obtained. Is it possible?
> 
> >> x=1:7;
> >> y=1:11;
> >> z=
> [0.3100    0.3393    0.3638    0.4013    0.3783    0.3485  
>  0.3258
>     0.3450    0.3996    0.4548    0.5188    0.4564    0.4052
>    0.3471
>     0.3704    0.4487    0.5299    0.6182    0.5357    0.4555
>    0.3769
>     0.3997    0.5052    0.6176    0.7382    0.6186    0.5185
>    0.4039
>     0.4279    0.5614    0.7074    0.8544    0.7155    0.5784
>    0.4389
>     0.4602    0.6335    0.8104    1.0000    0.8238    0.6521
>    0.4743
>     0.4372    0.5812    0.7335    0.8823    0.7279    0.5845
>    0.4327
>     0.4001    0.5199    0.6393    0.7660    0.6502    0.5318
>    0.4108
>     0.3769    0.4704    0.5695    0.6650    0.5740    0.4791
>    0.3816
>     0.3460    0.4139    0.4785    0.5481    0.4886    0.4199
>    0.3559
>     0.3197    0.3578    0.3943    0.4302    0.3958    0.3579
>    0.3212];

In theory, one could estimate the coefficients of
your model from data such as this. There are
several methods one might use, ranging from a
nonlinear regression to a transformation to a linear
regression problem. HOWEVER...
 
Do you realize that your model does not even come
REMOTELY close to having the correct shape for
this surface? Have you properly written down the
actual model that you will use?

John