what does :: mean and why is it not recognized by MatLab

This is in plot::SurfaceSTL

Answer 1

[Stephen23]

The :: indicates that it is NOT a MATLAB command, but is used in MuPAD (the symbolic math engine):

https://www.mathworks.com/discovery/mupad.html

https://www.mathworks.com/help/symbolic/getting-started-with-mupad.html

Answer 2

[Steven Lord]

Functions whose names include :: like plot::SurfaceSTL, or those whose documentation pages include a warning note like the one at the top of the plot::SurfaceSTL documentation page, are intended to be used in a MuPAD Notebook or using feval in conjunction with symengine. They are not intended to be called directly from the MATLAB command prompt or inside a MATLAB function.

[Walter Roberson]

evalin(symengine) can also be used

[John BG]

I completely agree with Mr Roberson. I like command evalin, very powerful, it enables dynamic generation of code, code that writes code.