fit_dat

Parameter identification based on measured data

Calling Sequence

[p,err]=fit_dat(G,p0,Z [,W] [,pmin,pmax] [,DG])

Arguments

G Scilab function (e=G(p,z), e:  nex1, p: npx1, z: nzx1)

: :p0 initial guess (size npx1) : :Z matrix [z_1,z_2,...z_n] where z_i (nzx1) is the ith measurement : :W weighting matrix of size nexne (optional; default 1) : :pmin lower bound on p (optional; size npx1) : :pmax upper bound on p (optional; size npx1) : :DG partial of G wrt p (optional; S=DG(p,z), S: nexnp) :

Description

fit_dat is used for fitting data to a model. For a given function G(p,z), this function finds the best vector of parameters p for approximating G(p,z_i)=0 for a set of measurement vectors z_i. Vector p is found by minimizing G(p,z_1)’WG(p,z_1)+G(p,z_2)’WG(p,z_2)+...+G(p,z_n)’WG(p,z_n)

Examples

function y=FF(x)
  y=a*(x-b)+c*x.*x;
endfunction
X=[];
Y=[];
a=34;
b=12;
c=14;
for x=0:.1:3
  Y=[Y,FF(x)+100*(`rand`_()-.5)];
  X=[X,x];
end
Z=[Y;X];
function e=G(p, z)
  a=p(1)
  b=p(2)
  c=p(3)
  y=z(1)
  x=z(2)
  e=y-FF(x)
endfunction

[p,err]=fit_dat(G,[3;5;10],Z)

`xset`_('window',0)
`clf`_();
`plot2d`_(X',Y',-1)
`plot2d`_(X',FF(X)',5,'002')
a=p(1);
b=p(2);
c=p(3);
`plot2d`_(X',FF(X)',12,'002')

a=34;
b=12;
c=14;
function s=DG(p, z)
  y=z(1),
  x=z(2),
  s=-[x-p(2),-p(1),x*x]
endfunction

[p,err]=fit_dat(G,[3;5;10],Z,DG)

`xset`_('window',1)
`clf`_();
`plot2d`_(X',Y',-1)
`plot2d`_(X',FF(X)',5,'002')
a=p(1);
b=p(2);
c=p(3);
`plot2d`_(X',FF(X)',12,'002')

See Also

• optim non-linear optimization routine
• datafit Parameter identification based on measured data