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IDL: Interactive Data Language

by Anu Rao

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Running IDL

To run idl, at the Unix prompt type

idl

To access idl's online help, at the idl prompt type

IDL> ?

and a separate, menu-driven help window will pop up. To run the built-in demo program, type

IDL> demo

and a separate window will pop up, with menu-driven options.

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IDL Examples

We have some sample IDL scripts available online:

• plots.pro and sine.dat; some examples of simple plots, multiple plots with various options
  • a simple sine curve
  • multiple plots using the !p.multi command, with different fonts and plot symbols
  • multiple plots using the position option, with logarithmic axes and postscript fonts
• loops.pro; example of "for" and "if-then-else" statements
• matrices.pro; some examples of array and matrix manipulation
• consurf.pro and mydata.dat; examples of contour and surface plots
  • simple contour plot
  • contour plot with 6 levels, labels
  • contour plot with 25 levels
  • surface plot with axis labels
  • surface plot with 3-D contours
  • shaded surface plot
  • shaded surface plot with lighting determined by height
  • overkill: combination surface/contour plots
• images.pro and calvin.gif; some image display and manipulation examples
  • here is the original image
  • smooth the image and add it to itself
  • subtract the max of the image from itself
  • apply a median filter

For example, to run the IDL script plots.pro, save the file plots.pro and sine.dat to you directory. Then run IDL, and type

IDL> .run plots

and a separate window will pop up with the plot.

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Helpful Hints/Notes for IDL

• To save a plot to a postscript file filename.ps, type the following commands:

          set_plot, 'ps'
          device, file='filename.ps'
          .
          .
          plot commands
          .
          .
          device, /close
  
  
  

  To print out the file filename.ps, at the Unix prompt type

  lpr filename.ps

• To run an idl script name.pro as a background job and store the output in the file name.out, at the Unix prompt type

  idl < name.pro > name.out &

• NOTE: The indices for arrays and matrices begin at 0
• To view the value of a variable foo, type

  IDL> print, foo

• To view detailed information about all variables being used, type

  IDL> help

• To view the available colormaps, type

  IDL> loadct

• To load in a colormap, either type loadct, #entrynumber or type xloadct and a window will pop up.
• The source code for the idl demos is not available. But there are some examples kept in the /usr/local/src/idl_4/examples/general directory.
• NOTE: This is a commercial package, and thus may not be readily available everywhere. There is a limited 7-minute demo version available for free, "for evaluation purposes."
• If you intend to use LOTS of colors, then do the following:
  1. create a file called .idl, containing the following lines:

       device, pseudo=8
       window, 0, colors=256, /pixmap
       wdelete, 0
     
     

  2. define the following environment variable in your start-up file (in cshell, .cshrc; in kshell, .profile)

     setenv IDL_STARTUP $HOME/.idl

• Some handy web sites:
  • The Research Systems, Inc IDL Page (the creators/marketers of IDL)
  • Some IDL Help from the LANL
  • An IDL FAQ