How can I export a 3D Graph from MATLAB to an .obj or .stl file?

I have created gyroid geometry using the following equation:

f = (@(x,y,z) sin((2*pi*x)/a).*cos((2*pi*y)/a)+sin((2*pi*y)/a).*cos((2*pi*z)/a)+sin((2*pi*z)/a).*cos((2*pi*x)/a)); fimplicit3(f,interval)

Interval is from -0.5 to 0.5 on all axes.

I am trying to use this function: https://www.mathworks.com/matlabcentral/fileexchange/20922-stlwrite-filename--varargin-

But I cannot seem to get it to work. Any help on how I can make it work. Thank you for your help.