fitting equation with condition on 1 parameter
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I have to fit an equation over my data. Equation has two unknows parameters to be found i.e a and b...but if i deliberately want that the b value should lie betweem 0.2 and 2 and then find 'a' and 'b'...how can i do that???
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Here is a simple script for fitting a Gaussian f(z) = a*exp(-b*z^2) using LSQCURVEFIT subject to bounds a>=0, 0<=b<=7. You should run it, study it, and adapt it to your needs.
f=@(p,z) p(1)*exp(-p(2)*z.^2);
x=linspace(0,2,10);
y=f([1,2],x)+rand(size(x))/10; %simulated data
p=lsqcurvefit( f, [.5,.5], x,y, [0,0],[inf,7]); %perform fit
plot(x,y,'*', x, f(p,x)) ;
You should also, of course, read "doc lsqcurvefit" to understand the input syntax and know what additional options you have.
7 个评论
aditi
2014-1-23
[.5,.5] is my initial guess of the parameters. You should see an explanation of that in "doc lsqcurvefit".
Bounds on individual parameters can be set to inf and -inf if you effectively want them unconstrained. You can see in my example that I set upper and lower bounds on a of 0 and inf, meaning that a is not bounded from above, but is constrained to be >=0.
aditi
2014-1-24
Matt J
2014-1-24
The curve isn't discontinuous. You're just not plotting it at very many points.
aditi
2014-1-24
Matt J
2014-1-24
Plot at more densely spaced points.
aditi
2014-1-24
更多回答（2 个）
Amit
2014-1-23
0 个投票
You can use fmincon.
I would think that these a and b are from you previous post, where fminsearch were used. fmincon is similar to fminsearch but support bounds. More details on fmincon is here http://www.mathworks.com/help/optim/ug/fmincon.html
Alan Weiss
2014-1-23
编辑：Alan Weiss
2014-1-23
0 个投票
There are some documentation examples that show how to fit equations. Adding bound constraints is easy for lsqnonlin or lsqcurvefit.
Hope this helps,
Alan Weiss
MATLAB mathematical toolbox documentation
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