Many functions are provided as m-files. You can view an m-file by using the type function at the command line. Thus
type pca
Thus, from the stats toolbox, I can view the course code for the pca function as above.
NEVER use edit on provided files like this, as it is too easy to accidentally make changes to the code, thereby creating a bug in that code. You would then need to download MATLAB again to repair the problem.
For compiled functions, source code is never provided. Period.
