What is IDL or slapping you around with facts

1
What is IDL?!?!(or slapping you around with
facts)

• IDL Tutorial Day 1
• Nick Hill
• hillnich_at_grinnell.edu

2
Main IDL Points

• IDL is just another programming language
• Much akin to FORTRAN
• We compute with it in a UNIX OS (UNIX and IDL are
  independent things, and IDL is just a program in
  UNIX)

3
UNIX Commands

• gtpwd gtshows the directory youre currently
  in
• gtcd path directory gt changes the directory
  location
• (ex
  cd /disk/drive/nhill)
• gtcp filename path gt copies files
• gtls gt lists files
  in a folder
• gtls sav gt lists files in folder
  ending with .sav
• gtssh -Y log-in gt secure shell log-in w/
  graphics
• gtmkdir folder gt makes a folder
• gtnedit gt opens nedit text editor
• gtnedit filename gt opens an already
  saved text file, other editors are
  emacs, vi, and pico

4
Starting IDL

• Any of the following prompts work
• gt idl
• gt sswidl
• - sswidl is loaded with path directories with
  useful solar software (ssw) programs and youll
  consequently use most often
• gt sswidlde
• - IDL is loaded with a GUI
• To enter UNIX command in IDL, use
• IDLgt ls sav
• Exceptions are cd and pwd
• IDLgt cd, /disk/data/bastille/
• IDLgt pwd
• To exit IDL, just exit
• IDLgt exit

5
Notes on Syntax

• UNIX is case sensitive, IDL is not
• Up arrow recalls recent IDL commands (down lets
  you subsequently cycle through them)
• Ctrla and ctrle take you to the beginning and
  end of command lines, respectively
• allows you to type multiple commands on one
  line
• IDLgt x fltarr(5) print, x
• Commas separate arguments in IDL!
• IDLgt plot, x, y, xtitle x, ytitle y
• Ctrl-c interrupts a running operation
• Use when your program is clearly taking longer
  than it should (ie infinite loop)
• continues a command line (useful in program
  code when commands get long)
• IDLgt for i 0,4 do
• IDLgt print, x(i)
• comments out everything the proceeds after it

6
Variables

• Types
• Integer, used mainly for loops or array indices
  (1, 3, 100, etc.)
• Floating, different from integer by decimal point
  (2.71, 3.14159)
• String, text stored as a variable
• Variables are assigned by equating some value on
  the right to text acting as a variable on the
  right
• IDLgt a 10000.
• IDLgt b 5.271
• IDLgt c I study fysics (note any text not a
  variable or command requires quote
  marks)
• Variations on variables
• Arrays, a bit like a matrix
• IDLgt z fltarr(5, 5) creates a 5x5
  matrix-array with 0. in all spots
• Structures, kind of unique to IDL (at least in my
  experience)
• Stores text, values, anything as one thing
• Often get these as a result of data from
  satellites

7
Variables, contd

• Variable names must begin with a letter
• Ie 8b is not an allowed variable name
• Variables cant have a space in them
• use underscores
• keeping spaces out of any names is just a good
  idea in UNIX world
• Dont name variables after IDL functions
• Ie print 7 is not a good idea
• All array, vector, and structure indices begin
  with zero
• multiplication
• / division
• addition
• - subtraction
• exponentiation

8
Help

• IDL help, ?
• IDLgt ?
• xdoc, opens a widget with solar software program
  code -EXTREMELY USEFUL. If a program crashes
  while youre in IDL, this wont function. You
  have to log out and back in
• IDLgt xdoc
• Whats the variable?
• IDLgt help, x
• IDLgt help, x, /str
• Wheres the program?
• IDLgt which, do_stuff.pro
• /disk/data/nhill/practice/do_stuff.pro
• Google
• Make mistakes and ask for help

9
Practice