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From: C. on 10 May 2010 06:58
I've got an equation with three independants f(x, y, z)= 1+A*B^x *C^y*sqrt(z).
I already fitted the equation to a surface with sftool, assuming y as a constant value but that won't give me correct values for A,B,C i think.
So what i need is a tool like sftool, but with the option to have 3 independants. Not important if that can't be displayed in some kind of diagram anymore..

Has anyone got an idea that could help me?
From: John D'Errico on 10 May 2010 09:05
"C. " <vogel.jan(a)googlemail.com> wrote in message <hs8osd$nk7$1(a)fred.mathworks.com>...
> I've got an equation with three independants f(x, y, z)= 1+A*B^x *C^y*sqrt(z).
> I already fitted the equation to a surface with sftool, assuming y as a constant value but that won't give me correct values for A,B,C i think.
> So what i need is a tool like sftool, but with the option to have 3 independants. Not important if that can't be displayed in some kind of diagram anymore..
>
> Has anyone got an idea that could help me?

It depends. Do you have

- The statistics toolbox? (nlinfit)
- The optimization toolbox? (lsqnonlin, lsqcurvefit)

Neither of them? Use fminsearch. Or transform the
problem to be able to use a linear regression. Or
download a tool from the file exchange.

Lots of ways to do this, but since I don't know what
you have, I can't advise you more.

John
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