That is(might be) a toolbox with a number of useful functions for solving and anlysing inverse problems, typically you should put that file somewhere "intelligently", so that you have all your toolboxes in a neat and organized structure. I do this by putting them in a separate directory in my matlab directory and then put in a line in my startup.m-file. Thisly:
in a standard shell: > mv regtools ~/matlab/Local/Numerics/regtools
into startup.m: addpath /home/bjorn/matlab/Local/Numerics/regtools -end
startup.m should reside in /home/bjorn/matlab/
HTH
