LOADPATH

DEFAULT_LOADPATH

which butter

ls /usr/share/octave/site/m/octave-forge/signal/butter.m

DEFAULT_LOADPATH = strcat( DEFAULT_LOADPATH, 
   ":/usr/share/octave/site/m//")

rehash

which butter

DEFAULT_LOADPATH = strcat( DEFAULT_LOADPATH, 
   ":/usr/share/octave/site/m/octave-forge//")

rehash

which butter