The program accepts as a parameter the a name of lattice (*.opt) file. This mechanism allows one to launch the program from the File Manager (a.k.a. Windows Explorer in Windows XP and later) by double clicking on a file with the *.opt extension; or simply from the command line prompt by typing the program file name and the OptiM file name e.g.
optim astrid.opt
To associate the *.opt extension (under MS Windows) involves the following steps
An equivalent procedure would have to be followed on other platforms.