I am looking for a simple version control system
    for use by one programmer writing a small MATLAB
    system with GUI. Is RCS suitable?

As Bob noted, RCS is a live single file-by-file VC system.  If you won't
have many source files involved, that will likely be fine.  If you want
something that actually does atomic commits of a group of files, it
wouldn't be right.

If you want an alternative, my personal recommendation would be
Subversion.  In my experience it is considerably simpler to understand
and use (less chance of errors) than git.  I won't go into the
technicalities unless you care.

However, any of git, subversion, cvs, etc., would undoubtedly be more
initial work to set up and get familiar with than RCS.

Happy version controlling,
Karl