lsqcurvefit Error using /

Hi, I'm trying to use MATLAB to fit some data using nonlinear least square fitting. When I run my code:

xdata = NbO2_219_T';        %NbO2_219_T is a column vector (want a row vector)
ydata = NbO2_219_ln_rho';   %NbO2_219_ln_rho is a column vector
fun = @(x,xdata) (x(1)*(1 + (sqrt(1 + xdata./x(2)) - 1)/(xdata./x(2))))/sqrt((sqrt(1 + xdata./x(2)) - 1)) + x(3);   
                                                          %x = [x(1) x(2) x(3)] Parameters to solve for
x0 = [5 7e-3 -30];                                        %Initial geusses for parameters
x = lsqcurvefit(fun,x0,xdata,ydata)

I get the following error:

Error using /

Matrix dimensions must agree.

Error in

nonlinearfit_rho_vs_T>@(x,xdata)(x(1)*(1+(sqrt(1+xdata/x(2))-1)/(xdata/x(2))))/sqrt((sqrt(1+xdata/x(2))-1))+x(3)

Error in lsqcurvefit (line 213)

initVals.F = feval(funfcn_x_xdata{3},xCurrent,XDATA,varargin{:});

Error in nonlinearfit_rho_vs_T (line 14)

x = lsqcurvefit(fun,x0,xdata,ydata)

Caused by:

Failure in initial objective function evaluation. LSQCURVEFIT cannot continue.

Does anyone know what could be the potential cause of this? I tried replacing the '/' with './' but unfortunately it did not solve the issue.

Answer 1

[Stephen23]

Replacing both of the mrdivide operators with rdivide operators gets rid of the error:

>> fun = @(x,xd) (x(1)*(1+(sqrt(1+xd./x(2))-1)./(xd./x(2))))./sqrt((sqrt(1+xd./x(2))-1))+x(3);
>> xdata = randi(9,1,7);
>> x0 = [5,7e-3,-30];
>> fun(x0,xdata(:))
ans =
  -28.376
  -28.678
  -28.914
  -28.376
  -28.376
  -28.979
  -29.029

Only you can decide if this is correct.

[Chris Andoh]

Thanks, it worked! I completely forgot about the "/" (mrdivide) in between the first term.