why do I see error in curve fitting?

What I try to run the below example given under the link : https://in.mathworks.com/help/curvefit/fit.html

clear; close all; clc;
load census;
f=fit(cdate,pop,'poly2');
plot(f,cdate,pop);

it throws following error...

Unable to resolve the name curvefit.attention.Error.

Error in fit>iCreateErrorFunction (line 631)
errorFcn = curvefit.attention.Error();

Error in fit (line 107)
errorFcn = iCreateErrorFunction( nargout > 4 );

Can anyone please help?

[KSSV]

What does

which fit 

/MATLAB/toolbox/curvefit/curvefit/fit.m

show?

[MP]

>> which fit

C:\Program Files\MATLAB\R2021a\toolbox\curvefit\curvefit\fit.m

[MP]

The curve fitting toolbox is located at C:\Program Files\MATLAB\R2021a\toolbox\curvefit\curvefit\fit.m

still it gives following error.

Error using cfit
'fittype' requires Curve Fitting Toolbox.

Error in fit>iFit (line 128)
fitobj = cfit;

Error in fit (line 116)
[fitobj, goodness, output, convmsg] = iFit( xdatain, ydatain, fittypeobj, ...

Answer 1

[Walter Roberson]

The Curve Fitting Toolbox needs to be reinstalled.

[MP]

I tried re-installing, it shows same error.

Is it possible to Copy-Paste C:\Program Files\MATLAB\R2021b\toolbox\curvefit folder from 2021B to C:\Program Files\MATLAB\R2021a\toolbox\curvefit to 2021A? and then Add path C:\Program Files\MATLAB\R2021a\toolbox\curvefit to matlab??

[Walter Roberson]

No, you cannot use code from a later toolbox together with an earlier MATLAB.

[MP]

Thank you for the clarification..

How about the other way round? I have 2017 matlab too.. Can I Copy-Paste 2017 toolbox to 2021 matlab folder and then add to 2021matlab path?

[Walter Roberson]

It is possible for that message to show up if you have the Curve Fitting Toolbox installed, but somehow do not have a license to use it.

For individual licenses, it is typically only possible to install toolboxes you have a license for, but there are some situations in which it is possible.