lsqcurvefit : undefined values at initial point
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a.mat contains the output of a ccd camera.
y = transpose(mean(a));
x = transpose(1:1280);
x0 = [600 1e4 .01];
parfit = lsqcurvefit(@fraunhof,x0,x,y)
function F = fraunhof(x,xdata)
beta = x(3).*(xdata-x(1));
sinbeta = sin(beta);
F = x(2).*sinbeta.^2./beta.^2;
Running this code returns the following error:
Error using snls (line 47)
Objective function is returning undefined values at initial point. lsqcurvefit cannot continue.
Error in lsqncommon (line 150)
[xC,FVAL,LAMBDA,JACOB,EXITFLAG,OUTPUT,msgData]=...
Error in lsqcurvefit (line 253)
[xCurrent,Resnorm,FVAL,EXITFLAG,OUTPUT,LAMBDA,JACOB] = ...
采纳的回答
Star Strider
2015-8-7
You’re encountering a ‘sin(x)/x’ problem, where your function is undefined at 0. The solution is to have it defined at 0, although you have to fudge your function a bit to do it. I added 1E-8 to ‘beta’ to emulate L’Hospital’s rule, and got a good fit:
fraunhof = @(x,xdata) x(2).*sin(x(3).*(xdata-x(1)) + 1E-8).^2./(x(3).*(xdata-x(1)) + 1E-8).^2;
x0 = [600 1E5 0.01];
parfit = lsqcurvefit(fraunhof,x0,x,y)
figure(1)
plot(x, y)
hold on
plot(x, fraunhof(parfit,x))
hold off
grid
parfit =
649.6130e+000 47.9481e+003 10.3101e-003
5 个评论
G Guerrer
2015-8-10
Star Strider
2015-8-10
My pleasure!
Josh Begale
2019-2-18
I am having a similar issue with my code and was wondering if you could assist me? Here is my code and following errors:
F1 = @(x,xdata)(x(1)*(xdata.^2 - xdata.^(-1))); %% Neo-Hookean
F2 = @(x,xdata)(2*(x(1)*(xdata.^2 - xdata.^(-1)) + x(2)*(xdata - xdata.^(-2)))); %% Mooney-Rivlin
F3 = @(x,xdata)((x(1)/x(2))*(xdata.^x(2) - xdata.^(-x(2)/2))); % Ogden
NH1 = lsqcurvefit(F1,[1,1,1],S,MP);
% NH2 = lsqcurvefit(F1,[1,1,1],S,LP);
% MR1 = lsqcurvefit(F2,[1,1,1],S,MP);
% MR2 = lsqcurvefit(F2,[1,1,1],S,LP);
% Og1 = lsqcurvefit(F3,[1,1,1],S,MP);
% Og2 = lsqcurvefit(F3,[1,1,1],S,LP);
Error using snls (line 47)
Objective function is returning undefined values
at initial point. lsqcurvefit cannot continue.
Error in lsqncommon (line 166)
snls(funfcn,xC,lb,ub,flags.verbosity,options,defaultopt,initVals.F,initVals.J,caller,
...
Error in lsqcurvefit (line 257)
lsqncommon(funfcn,xCurrent,lb,ub,options,defaultopt,caller,...
Error in Matlab_Code (line 5)
NH1 = lsqcurvefit(F1,[1,1,1],S,MP);
Star Strider
2019-2-18
@Josh Begale — It would be best for you to post this as a new Question, then delete this Comment.
更多回答（1 个）
When xdata(i)=x(1) or x(3)=0, then beta(i) will be zero and your expression for F
F = x(2).*sinbeta.^2./beta.^2
is undefined.
Similarly, if xdata is being assigned the uint16 variable "a" in your a.mat file, then any operation xdata(i)-x(1) will evaluate to 0 when x(1)>xdata(i). My guess is that this is what's happening, in which case you should cast a to double precision.
4 个评论
I now see that your xdata=1:1280
This means that xdata(600)=600. Since x(1)=600 at your initial point, this will give F(600)=0/0=NaN in your objective function.
Presumably you want F=0 when beta=0? If so, add some post-processing
F(beta==0)=0;
G Guerrer
2015-8-7
G Guerrer
2015-8-7
Matt J
2015-8-7
Try this simple experiment at the command line.
>> beta=0; sin(beta)/beta
ans =
NaN
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