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From: John on 10 Feb 2010 22:50
If I have an x,y,z matrix such as:
x y z
1 10 500
2 10 700
3 10 800
1 20 750
2 20 850
3 20 950

How can I correctly implement the LSQCURVEFIT command:
X = LSQCURVEFIT(FUN,X0,XDATA,YDATA,LB,UB,OPTIONS)
I need the equation relating these points in a 3d space so i can create a nice surf or mesh plot.

Inside the function fun, I want to use the cost function:
F = a(1)*x + a(2)*y + a(3)*x*y + a(4)*x^2*y +a(5)*x*y^2
to find the coefficients.
and Initially set XO=0.

Be excellent to each other and party on.
From: John D'Errico on 10 Feb 2010 23:49
"John " <tarpoon7(a)gmail.com> wrote in message <hkvups$sr1$1(a)fred.mathworks.com>...
> If I have an x,y,z matrix such as:
> x y z
> 1 10 500
> 2 10 700
> 3 10 800
> 1 20 750
> 2 20 850
> 3 20 950
>
> How can I correctly implement the LSQCURVEFIT command:
> X = LSQCURVEFIT(FUN,X0,XDATA,YDATA,LB,UB,OPTIONS)
> I need the equation relating these points in a 3d space so i can create a nice surf or mesh plot.
>
> Inside the function fun, I want to use the cost function:
> F = a(1)*x + a(2)*y + a(3)*x*y + a(4)*x^2*y +a(5)*x*y^2
> to find the coefficients.
> and Initially set XO=0.
>
> Be excellent to each other and party on.

Don't bother using lsqcurvefit here. Why use a nonlinear
regression tool to fit a linear model? Then you need to
provide starting values, a silly thing if they are not
really needed.

Just download polyfitn from the file exchange.

http://www.mathworks.com/matlabcentral/fileexchange/10065

John
From: awu PROM on 28 Feb 2010 12:07
Dear John
I can not run your polyfitn.m file.
There is still an error
??? Error: File: C:\MATLAB6p1\work\polyfitn.m Line: 141 Column: 24
Expected a variable, function, or constant, found "|".
Could you fix it?

"John " <tarpoon7(a)gmail.com> wrote in message <hkvups$sr1$1(a)fred.mathworks.com>...
> If I have an x,y,z matrix such as:
> x y z
> 1 10 500
> 2 10 700
> 3 10 800
> 1 20 750
> 2 20 850
> 3 20 950
>
> How can I correctly implement the LSQCURVEFIT command:
> X = LSQCURVEFIT(FUN,X0,XDATA,YDATA,LB,UB,OPTIONS)
> I need the equation relating these points in a 3d space so i can create a nice surf or mesh plot.
>
> Inside the function fun, I want to use the cost function:
> F = a(1)*x + a(2)*y + a(3)*x*y + a(4)*x^2*y +a(5)*x*y^2
> to find the coefficients.
> and Initially set XO=0.
>
> Be excellent to each other and party on.
From: John D'Errico on 28 Feb 2010 12:22
"awu PROM" <arwut365(a)hotmail.com> wrote in message <hme7rq$nub$1(a)fred.mathworks.com>...
> Dear John
> I can not run your polyfitn.m file.
> There is still an error
> ??? Error: File: C:\MATLAB6p1\work\polyfitn.m Line: 141 Column: 24
> Expected a variable, function, or constant, found "|".
> Could you fix it?

Can I fix it? Your matlab release is now about 10 years
old if you are using version 6.1. Polyfitn was written
since then, and it uses some things that were added
to matlab. Sorry, I can't go back and make polyfitn
run on your release, as it would then be less efficient
for the thousands of people who use more modern
releases.

You can choose to go through the code and figure
out what it does, repairing that which fails for your
release. This would be possible I imagine, but hardly
worth it. Instead, use another tool. Do you have the
stats toolbox? If so, then use regress.

Or, you can use backslash, or lscov, or lsqr, or a
variety of other tools already in matlab. Each of
these tools will require you to build the design
matrix for this problem, and so learn something
about linear regression in the process.

John
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