I'm not sure why this page is of no help whatsoever. It says:
On all platforms, you can also specify startup options using a MATLAB startup file?see Specifying Startup Options in the MATLAB Startup File
and that section of the page says:
Specifying Startup Options in the MATLAB Startup File
At startup, MATLAB automatically executes the file matlabrc.m and, if it exists, startup.m. The file matlabrc.m, which is in the matlabroot/toolbox/local folder, is reserved for use by MathWorks® and by the system manager on multiuser systems.
The file startup.m is for you to specify startup options. For example, you can modify the default search path, predefine variables in your workspace, or define defaults for Handle Graphics® objects. Use the following statements in a startup.m file to add the specified folder, /home/username/mytools, to the search path, and to change the current folder to mytools upon startup.
addpath /home/username/mytools cd /home/username/mytools
Place the startup.m file in the default or current startup folder, which is where MATLAB first looks for it. For more information, see MATLAB Startup Folder.