MATLAB Error fitting Stable distribution to data - Help?

MATLAB returns an unknown error every time I try to fit the Stable distribution to a dataset. I haven't encountered this error with previous datasets or MATLAB versions, but it has been 6 months since I've tried. This time I've used multiple data sets and confirmed that a Normal distribution will fit the datasets...but when I specify 'Stable' vice 'Normal', I get the following error:

"Unrecognized function or variable 'getIpOptions'.

Error in fmincon (line 832)

options =

getIpOptions(options,sizes.nVar,mEq,flags.constr,defaultopt,10,0.01);"

This code runs:

load hospital; % get MATLAB dataset
z = hospital.Weight; % Assign data values
pd = fitdist(z,'Normal');

However, this doesn't and returns the above error:

pd2 = fitdist(z,'Stable');

Is this a bug in the 2020a release?

I'm running:

>> version

ans = '9.8.0.1323502 (R2020a)'

Answer 1

[colordepth]

Optimization Toolbox is required for using the 'Stable' distribution with 'fitdist'. If the toolbox is already installed, I suggest re-installing it and trying again. Refer to the following related discussions for more information and workarounds if Optimization Toolbox is not available:

1. https://www.mathworks.com/matlabcentral/answers/491764-unrecognized-function-or-variable-getipoptions#comment_1889150
2. https://www.mathworks.com/matlabcentral/answers/545267-error-in-fmincon-getipoptions-is-coming-as-unrecognized-function-or-variable#comment_894665