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multistart with matlab function

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pirruccio giuseppe
pirruccio giuseppe on 8 Jul 2020
Commented: Walter Roberson on 13 Jul 2020 at 1:58
Hello everyone,
i am using lsqcurvefit for fitting some data i have. The code i wrote is the following:
[x, resnorm, residual, exitflag, output] = lsqcurvefit(@(x,xdata)myfun(x,xdata,E_x,Gamma_X,Gamma_C), x0, xdata, ydata, lb, ub, options);
with given x0, E_x, Gamma_X, Gamma_C, lb and ub. The function myfun is in an another file called myfun.m. The fit works fine but I noticed that the result depends on the choice of the initial guess x0. So i tried to implement a multistart. The code i tried to write based on the examples on the help page is the following:
problem = createOptimProblem('lsqcurvefit','x0',x0,'objective',@myfun,'xdata',xdata,'ydata',ydata);
ms = MultiStart('PlotFcns',@gsplotbestf);
[xmulti,errormulti] = run(ms,problem,50)
This code does not work, it gives me the following error:
Error in myfun (line 9)
F(1,:) = real((E_c + E_x - j*(Gamma_X - Gamma_C))/2 + 1/2*sqrt((E_c - E_x - j*(Gamma_X - Gamma_C)).^2 + 4*par(2).^2));
Error in lsqcurvefit (line 202)
initVals.F = feval(funfcn_x_xdata{3},xCurrent,XDATA,varargin{:});
Error in fmultistart
Error in MultiStart/run (line 260)
Error in CHO_matlab (line 91)
[xmulti,errormulti] = run(ms,problem,50)
Caused by:
Failure in initial objective function evaluation. LSQCURVEFIT cannot continue.
Failure in call to the local solver with supplied problem structure.
My understanding is that the function myfun within problem is missing the inputs parameters. Maybe there is also some other mistake which i do not know. So i replaced @myfun with @myfun(x,xdata,E_x,Gamma_X,Gamma_C) but now i get this error:
Unbalanced or unexpected parenthesis or bracket.
I also tried other similar combinations but noone seems to be acceptable.
What can i do it to make it work? How should i call the function with all the needed parameters?
Thank you all


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Accepted Answer

Alan Weiss
Alan Weiss on 9 Jul 2020
You almost had it right. Your objective function is
where the arguments E_x,Gamma_X,Gamma_C must already be in your workspace when you call createOptimProblem.
Alan Weiss
MATLAB mathematical toolbox documentation


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pirruccio giuseppe
pirruccio giuseppe on 13 Jul 2020 at 0:53
Ok thanks, so multistart already generates a set of different starting points each time it runs. Correct?
Walter Roberson
Walter Roberson on 13 Jul 2020 at 1:58
When you pass in an integer number of starting points like you do, then Yes, the starting points will be randomized except for x0

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