- Make sure there's nothing in the new path whose name conflicts with some pre-existing function
- Go File --> Set Path...
- Browse for the path you wish to permanently add to MATLAB's search path
- Add it
Or alternatively... (and subsequently, more dangerously)
At the MATLAB prompt, type:
>> open pathdef
In the m-file that appears, add the following to the big list of paths:
matlabroot,'your_path_from_MATLAB_root_directory:', ...
Don't touch anything else in the pathdef file. DON'T!