USE

filename

 The default file extension is .PCM
 If the filename is a text variable, it is first replaced by its value.

 VMS:  If filename is a logical name, it is replaced by its translation.
       If filename does not contain a file name extension, the default
       file name extension is appended to filename. Finally, if filename
       doesn't exist in the current directory, and if the logical name
       PHYSICA$LIB has been defined, that location is checked.

 UNIX: If filename is an environment variable, it is replaced by its 
       translation. If filename cannot be found in the current location,
       filename with the default file extension appended is checked. If
       this file cannot be found, and if the environment variable
       PHYSICA_LIB has been defined, then PHYSICA_LIB/filename is tried.
       Finally, if this file cannot be found, then PHYSICA_LIB/filename
       with the default file name extension appended is tried.