lsqcurvefit help

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zhengz
zhengz 2011-5-19
回答： MUMATZ QURESHI 2019-4-18
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.

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采纳的回答

Andrew Newell
Andrew Newell 2011-5-19
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 个评论
zhengz
zhengz 2011-5-19
You are the man! I tried both ways. They all work.

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更多回答（3 个）

MUMATZ QURESHI
MUMATZ QURESHI 2019-4-18
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 2013-2-17
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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