To install the 'libml' library (and a utility library 'libmisc'), you
can simply type
        make libml libmisc

You can also compile matls without changing the Makefile:
        make matls

If you also want the other example programs, you have to make slight
changes to the Makefile.

For mat2mat, you must decide what kind of regular expressions to use.
The GNU REGEX library is most convenient, but not required.  The default
is to use the built-in regular expression library used by ed(1).  If you
already have and want to use the GNU library, edit the Makefile
appropriately.  Then say
        make mat2mat

For pgm2mat, you must tell the Makefile where the PBMPLUS include files
and libraries are.  Then say
        make pgm2mat