|   | Licence type | Link | Notes |   | 
 
    
  | Full IDL licence | ITT (aka RSI) | Bloody expensive! Educational and bulk-buying discounts are available. | 
 
  
    
  | IDL student edition | ITT (aka RSI) | A very slightly older version of IDL is available for $100, for students
    pursuing degrees at high schools, colleges and universities. | 
 
 
    
  | Trial IDL licence | ITT (aka RSI) | If you run IDL without a licence, it works (almost) compleletly for seven 
    minutes, then quits. Saving is about the only thing that is disabled, to
    prevent you pre-compiling code to work with the options below.
    Of course, there's nothing stopping you writing your resutls to screen as
    text, then piping that into an external file. | 
 
  
    
  | IDL Virtual Machine | ITT (aka RSI) | If you can access one full IDL 6.0+ licence to compile and save IDL code,
    you can then run the code multiple times using this free utility. It is
    intended so that industrially-developed IDL code can be distributed in
    pre-compiled (and therefore un-stealable) form. Of course, the code has to
    be compiled on the same platform as it is later run. The only disadvantage
    is that a pop-up splash window appears before the code is started, making
    massive parallelisation impractical. | 
 
   
    
  | IDL runtime licence | N/A | This is essentially a version of the IDL Virtual Machine with a small cost
    but without the splash screen. It's therefore very useful for
    simultaneously running many jobs on a supercomputer. It doesn't appear to
    be very well advertised on RSI's web site: see the "Runtime Licensing"
    section of the "Building IDL Applications" manual, which is included in
    the free IDL download, or may posisbly be available from this link.
    You cannot pass any variables into the pre-compiled script by ordinary
    IDL means. To pass variables into the script so that it can do different 
    things in each instance, one workaround is to first set global system 
    variables, then access them from within IDL via 
    "spawn,'echo $VARIABLE',variable". | 
 
  
    
  | GDL (GNU Data Language) | Sourceforge | An attempt to build a free, open-source version of IDL. Its compatability 
    with complicated procedures is rather patchy at the moment, but improving.
    If you get it to work, please let me know! |