Alternatives to IDL licences:

Unfortunately, IDL licences are very expensive! If you or your department don't already have access to IDL, there are a few more affordable solutions. These all have limitations, but can be especially useful if you have to run code simultaneously on many processors.

  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!

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