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function demo_datafit()
demo_help demo_datafit
//create the experimental data
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];
//show the data points
xbasc();
SetPosition();
set figure_style old;
//xset("wpos",500,16);xset("wdim",600*0.9,400*0.9);xselect()
plot2d(X',Y',style=-1,leg='Donnes exprimentales')
realtimeinit(0.1);for k=1:30,realtime(k),end
// solve the non linear data fitting
[p,err]=datafit(G,Z,[3;5;10])
// show the fitting curve
plot2d(X',FF(X)',[5,2],'002','Fonction approximante')
realtimeinit(0.1);for k=1:30,realtime(k),end
xdel();
endfunction
function y=FF(x)
//parametric function model
y=a*(x-b)+c*x.*x,
endfunction
function e=G(p,z)
//datafit external computes the error
a=p(1),
b=p(2),
c=p(3),
y=z(1),
x=z(2),
e=y-FF(x)
endfunction
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