lsqcurvefit cannot evaluate initial function, says insufficient input arguments

I have a dataset described by a decaying exponential, I am trying to use lsqcurvefit to fit to this data. I have an anonymous function that plots a decaying exponential just fine, but I get errors like:

Not enough input arguments.

Error in
fitFID>@(amp,tConst,w,phi,offset,x)amp.*exp(-tConst.*x).*cos(w.*x+phi)+offset
(line 33)
FID = @(amp,tConst,w,phi,offset,x) amp.*exp(-tConst.*x).*cos(w.*x + phi)
+ offset;

Error in lsqcurvefit (line 213)
            initVals.F =
            feval(funfcn_x_xdata{3},xCurrent,XDATA,varargin{:});

Error in fitFID (line 35)%fitFID is the code shown below
par = lsqcurvefit(FID,par0,fitTime,fitData,[],[],opts);

Error in freeInductionDecay (line 75)%this is the code that calls the fitFID code
par = fitFID(data,extPar,1);

Caused by:
    Failure in initial objective function evaluation. LSQCURVEFIT cannot
    continue.
    

Here is the code:

    %data is a 4x1000000 double
x = data(2,:)';
time = data(4,:)';

%extPar.whatever are all just numbers to help with initial guesses
firstFitPoint = round((extPar.numCycles./extPar.centerFreq).*...
    ((extPar.endPoint - (extPar.firstPoint - 1))./(extPar.timebase.*10)));

fitData = x(firstFitPoint:end);
fitTime = time(firstFitPoint:end);%trims data to interesting part (i.e the decying part)
%% %%%%%%%%%%%%%%%%%%%Estimate parameters and perform fit%%%%%%%%%%%%%%%%%%
opts = optimset(...
    'TolFun',eps,...
    'MaxFunEvals',10000,...
    'Display','off',...
    'TolX',eps);

ampGuess = abs(max(fitData) - min(fitData));%estimate amplitude

tConstGuess = 25;%I don't have a good way to estimate this, so this one is hard-coded

wGuess = 2.*extPar.demodOffset;%estimate frequency

offsetGuess = mean(fitData);%estimate offset

par0 = [ampGuess,tConstGuess,wGuess,0,offsetGuess];%initial parameter set

FID = @(amp,tConst,w,phi,offset,x) amp.*exp(-tConst.*x).*cos(w.*x + phi) + offset;%function

par = lsqcurvefit(FID,par0,fitTime,fitData,[],[],opts);%perform fit

This issue was resolved by Stephan, below. lsqcurvefit assumes the function only has two inputs, one for parameters and one for the variable. The above code would work if the anonymous functino were replaced by:

%par = [amp,tConst,w,phi,offset] to keep track of parameters
FID = @(par,x) par(1).*exp(-par(2).*x).*cos(par(3).*x + par(4)) + par(5);%function

Answer 1

[Stephan]

Have a read here:

https://de.mathworks.com/matlabcentral/answers/465406-fmincon-error-not-enough-input-arguments

it appears to be the same issue - the keyword is "passing extra parameters"

[Wolfgang Klassen]

Thank you very much! That was indeed the issue. In order to use lsqcurvefit, the anonymous function has to be of the form @(par(:),x), not @(par(1),par(2),par(3),par(4),x), for example.