IDL Tutorial: Day 2

1
IDL Tutorial Day 2
Goals1) Introduce functions and procedures2)
Describe writing the simplest kind of programs 3)
Explain saving and restoring

• Angela Des Jardins
• (desjardins_at_physics.montana.edu)

2
Functions and Procedures

• Two basic types of programs
• Functions
• resultfunction_name(parameter, KeywordSet, )
• Examples size, n_elements, sin, cos, reverse,
  where
• - Functions can be placed anywhere you can put a
  value
• Procedures
• procedure_name, param1, param2, KeywordSet
• Examples help, print, open, printf, plot,
  set_plot, device, save
• - Procedures do stuff, but dont need to return
  a value
• Exact syntax for particular Procedures or
  Functions can be found using the help menu, xdoc,
  or the doc_library procedure

3
Commonly Used Procedures

• print for printing stuff to screen IDLgtprint,
  sin(x)
• plot plot variables to the current graphics
  device (usually screen) IDLgtplot, x,
  y,titleblah,keywords
• set_plot tells idl where to send plots to.
  Screen (Xdisplay) is default
• - IDLgtset_plot,x sends output to the x
  display
• - IDLgtset_plot, ps sends the output to a
  postscript file with default name idl.ps. Read ps
  files with ghostview
• unix_promptgt gv idl.ps
• device changes properties of the device
  currently enabled by set_plot. See help menu.

4
Save and Restore

• Programs are saved by saving the text file you
  write them in
• Save, the procedure, allows you to save variables
  to a file
• Example
• IDLgtsave, variable1, variable1, filefile.sav
• Restore allows you to restore saved variables to
  a session
• Example
• restore, file.sav

5
Commonly Used Functions

• Many math operators are functions
• IDLgt ysin(x) IDLgt ycos(x) IDLgtyexp(x)
• Where allows you to pick out the index of an
  array that meets some criterion
• gt indexwhere(new_array eq 15)
• (more on boolean operators later)
• Replicate makes copies of variables, arrays,
  structures, etc...
• gt starsreplicate(stars,15)
• dialog_pickfile allows you to graphically pick
  out file names
• gt file_namedialog_pickfile()

6
Macros (Scripts)

• Simplest form of Program
• In the editor window write commands just like you
  would at command prompt
• At the end type END so IDL knows when program is
  over
• Save the program with a unique name (i.e. save
  the text file)
• At the command prompt type either
• gt .run program_name
• gt .rnew program_name
• Shortcoming no loops allowed in macros.

7
Homework

• Make a macro in which you plot, on a good scale,
  with labels, yex. Also, have it print to the
  screen, You did it right! Make a post script
  copy of your plot.
• Make a file using emacs (or your favorite editor)
  which contains a row for each student in this
  class and a column for each of the following
  distance (in miles) of the students home from
  Bozeman, year in college, favorite color (in
  Angstroms), number of books read in the last
  year, number of trails hiked in the last year,
  and number of foods disliked . Use ascii_template
  and read_ascii to make a structure containing
  your numbers. Using the plot procedure, find out
  if there are any correlations among yourselves!