lsqcurvefit help

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zhengz
zhengz on 19 May 2011
Answered: MUMATZ QURESHI on 18 Apr 2019
I am absolutely new to MATLAB. I have 15 data sets and want to do a curve fitting to extract some parameters. Seems lsqcurvefit can do the job. First I tried to run the lsqcurvefit example in MATLAB. I copy and paste the code from the help file to a .m file like this:
function F = myfun(x,xdata)
F = x(1)*exp(x(2)*xdata);
% Assume you determined xdata and ydata experimentally
xdata = [0.9 1.5 13.8 19.8 24.1 28.2 35.2 60.3 74.6 81.3];
ydata = [455.2 428.6 124.1 67.3 43.2 28.1 13.1 -0.4 -1.3 -1.5];
x0 = [100; -1];
[x] = lsqcurvefit(@myfun,x0,xdata,ydata);
When I trie to run the code, it says something like this in the command windows:
??? Input argument "x" is undefined.
Error in ==> test1 at 3 F = x(1)*exp(x(2)*xdata);
What do I miss here? I know I need to get a book to study MATLAB. But I need to solve the problem as soon as possible. Thanks for help.

Accepted Answer

Andrew Newell
Andrew Newell on 19 May 2011
Maybe you have all of the code in one file? The function myfun should be in a separate file. Or you could use an anonymous function:
myfun = @(x,xdata) x(1)*exp(x(2)*xdata);
% Assume you determined xdata and ydata experimentally
xdata = [0.9 1.5 13.8 19.8 24.1 28.2 35.2 60.3 74.6 81.3];
ydata = [455.2 428.6 124.1 67.3 43.2 28.1 13.1 -0.4 -1.3 -1.5];
x0 = [100; -1];
[x] = lsqcurvefit(myfun,x0,xdata,ydata);
  1 Comment
zhengz
zhengz on 19 May 2011
You are the man! I tried both ways. They all work.

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More Answers (3)

MUMATZ QURESHI
MUMATZ QURESHI on 18 Apr 2019
function myfun
xdata = [0.9 1.5 13.8 19.8 24.1 28.2 35.2 60.3 74.6 81.3];
ydata = [455.2 428.6 124.1 67.3 43.2 28.1 13.1 -0.4 -1.3 -1.5];
x0 = [100, -1]; % Starting guess
x = lsqcurvefit(@myfun1,x0,xdata,ydata)
times = linspace(xdata(1),xdata(end));
figure;plot(xdata,ydata,'ko',times,myfun1(x,times),'b-')
legend('Data','Fitted exponential')
title('Data and Fitted Curve')
end
function F = myfun1(x,xdata)
F= x(1).*exp(x(2).*xdata);
end

Milad
Milad on 17 Feb 2013
Solved mine to, thanks

Daniela Garza Niño de Rivera
my code is not working is says :
" Error in Problem5M2>FunToFitM2 (line 12)
A=p(1);B=p(2);C=p(3);D=p(4);
Error in lsqcurvefit (line 213)
initVals.F = feval(funfcn_x_xdata{3},xCurrent,XDATA,varargin{:});
Error in Problem5M2 (line 6)
[P]=lsqcurvefit(@FunToFitM2,P0,T,muP);
Caused by:
Failure in initial objective function evaluation. LSQCURVEFIT cannot continue.
>> ""
how can i fix it?
here is the code:
function[P]=Problem5M2()
V= [275,10.52;277.2,8.702;279.4,6.887;281.7,5.071;283.9,3.705;286.1,3.164;288.3,2.603;290.6,2.053;292.8,1.502;295,1.306];
T=V(:,1); muP=V(:,2);
P0=[1;1];
[P]=lsqcurvefit(@FunToFitM2,P0,T,muP);
A=P(1);B=P(2);C=P(3);D=P(4);
P2=[A;B;C;D];
end
function[muP]=FunToFitM2(p,T)
A=p(1);B=p(2);C=p(3);D=p(4);
muP=(10).^(A+B./(T+C)+(D.*(T)));
end

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