'erfi' not found in my MATLAB while it is in the MathWorks

I tried to use erfi in my user-defined function, but there showed an error:

"Undefined function 'erfi' for input arguments of type 'double'.

I searched for erfi by 'help erfi', then it gives

"erfi not found. Showing help for erf instead ..."

However, I can find erfi on the MathWorks. The url is https://www.mathworks.com/help/symbolic/sym.erfi.html

and on the version history it is said to be "introduced on R2013a". My MATLAB version is R2021a.

I do not have the Symbolic Math Toolbox so I cannot compute it by integral either.

Please tell me if I can activate this should-be-embedded function.

Answer 1

[John D'Errico]

which erfi -all

/MATLAB/toolbox/symbolic/symbolic/@double/erfi.m  % double method
/MATLAB/toolbox/symbolic/symbolic/@single/erfi.m  % single method
/MATLAB/toolbox/symbolic/symbolic/@sym/erfi.m     % sym method
erfi is a built-in method                         % matlab.unittest.Verbosity method
erfi is a built-in method                         % matlab.unittest.internal.fixtures.FolderScope method

erfi is part of the symbolic toolbox.

It is NOT part of MATLAB proper. If you don't have the symbolic toolbox, then you don't have erfi. If you need it, then you need that toolbox.