Fwd: fitting circle to data

[Gastón Araguás]

Somebody in the list told me that the function i'm using to minimize
doesn't depends on x
xt = %data
yt = %data

F = @(x,a) (xt-a(1)).^2+(yt-a(2)).^2-a(3).^2

so i try to put it in this way

F = @(x,a) (x(1)-a(1)).^2+(x(2)-a(2)).^2-a(3).^2
pin = [1; 1; 1];
[f , p] = leasqr([xt yt],zeros(size(xt)),pin,F);

but i get:
warning: inverse: matrix singular to machine precision, rcond = 7.27849e-18
error: number of rows must match (1 != 388) near line 324, column 18
error: evaluating argument list element number 1
error: evaluating assignment expression near line 324, column 2
error: called from `leasqr' in file
`/usr/share/octave/packages/3.0/optim-1.0.5/leasqr.m'

i can't find my mistake, i think the data sizes are ok

size([xt yt])
ans =

   388     2

size(zeros(size(xt)))
ans =

   388     1

thank you very much




---------- Forwarded message ----------
From: Gastón Araguás <address@hidden>
Date: 2009/12/1
Subject: Re: fitting circle to data
To: address@hidden


Thank you very much to all. This code is working well now:

xt = %data
yt = %data

F = @(x,a) (xt-a(1)).^2+(yt-a(2)).^2-a(3).^2
pin = [1;1;1];
[f , p] = leasqr(xt,yt,pin,F);

p =

  8.2224e-02
  2.4914e+02
  2.3772e+02   <---- r

on the other hand this linear version gives good results too, without
initializations (thanks to Richardson)

A = [ xt yt ones(size(xt))];
b = xt.^2 + yt.^2;
c = A\b;

r = sqrt(c(3) + c(1)^2 + c(2)^2);
r =  238.25

I'm not sure wich of them is the best result, I'll try to test it with
real and artifcial data

Thank you all again

--
Gastón Araguás
______________________________________________________
CIII - Centro de Investigación en Informática para la Ingeniería
Univ. Tecnológica Nacional Facultad Regional Córdoba. Argentina



-- 
Gastón Araguás
______________________________________________________
CIII - Centro de Investigación en Informática para la Ingeniería
Univ. Tecnológica Nacional Facultad Regional Córdoba. Argentina