IDL Tutorials: Day 1

1
IDL Tutorials Day 1

• Michael Hahn
• (hahn_at_solar.physics.montana.edu)

2
What is IDL

• Interactive Data Language- for easy manipulation
  of large data sets
• Many useful functions already in large library
• Used by
• - Nasa
• - Lockheed-Martin
• - Medical Imaging
• http//www.rsinc.com/
• http//idlastro.gsfc.nasa.gov/homepage.html
• http//www.astro.washington.edu/deutsch/idl/htmlhe
  lp/index.html
• http//www.ugastro.berkeley.edu/tutorials/tutorial
  s.html
• http//www.lmsal.com/solarsoft

3
General Strategies

• Know the problem before you start programming
• Search to see if a similar problem has already
  been solved
• -IDL help menu (gt?)
• - xdoc (sswidl)
• Dont Memorize
• Use the help Screen
• Keep notes on your work
• Write programs in steps
• Learn by doing

4
Using sswidl(de) and Help

• SSW solar software, useful for solar physicists
• Calling sswidl or sswidlde calls IDL with
  specified paths
• - paths with useful programs for solar physics
  work
• To manually set paths talk to _______________
• Calling sswidlde calls a developer
• - graphical interface
• - real time information about your code
• Any text editor can be used
• - nedit, emacs, pico, vi
• gt? Calls up help index for information on
  procedures
• Help, variable, for properties of variable
  or status

5
Journal Procedure

• Records everything you enter into a textfile
• Syntax
• IDLgt journal, text_file opens the file
  starts record
• IDLgt command line statements
• IDLgt journal closes the file
• IDL is not case sensitive but Unix is
• IDLgt help, var IDLgt HELP, Var
• but IDLgt journal, text_file ? Journal,
  Text_File
• Open journal file with any text editor
• nedit text_file

6
Basic Variable Types

• Strings
• - Text
• - Must be contained within or
• - cannot perform numerical operations
• Integers
• - only range from 32,768 to 32,767
• Longword Integers
• - long() for 32 bit integers
• - long64() for 62 bit integers
• Float
• - floating point number with 32 bit word length
• Double
• - a floating point number with 64 bit word
  length

7
Assigning a Variable a Value

• Variable_name value
• - will automatically select a variable type
• variable_name function_name(argument)
• Variable_namestring(value)
• Variable_name long(value)
• Variable_name fix(value) (for integers)
• Variable_name double(value)

8
Naming Variables

• Assign readable variable names that make sense
• Variable names must start with a letter
• - NO 6agamma OK a6gamma
• Variables should not have the same name as IDL
  functions
• - NO plot6.0
• Variable names may not have spaces in them
• - NO A 65 OK A_65
• Some characters are illegal or have special
  meanings
• - NO a_at_5, a.b5 (used for structures), A5,
  A5

9
Arrays

• Variables, of any type, that contain multiple
  values
• Array Indexing IDL arrays start at index zero
• - e.g. A1,2,3,4 print, A0 1 print,
  A1 2
• Multiple ways to create arrays
• intarr(), fltarr(), dblarr(), strarr()
• indgen(), findgen(), dindgen()
• - Look up the above in the IDL help (e.g. gt?
  Intarr)
• Array operations, see the help menu or experiment

10
Structures

• Structures are variables that contain multiple
  variables
• (scalars, arrays, or other structures)
• Each variable contained within a structure is
  called a tag
• Syntax structstruct_type, tag_name1
  tag_value1,
• e.g.
• Starsstar_name, Namealpha centauri a,
• spec_typeg2 V, coords14 38.0, -60
  44,
• Distancedouble(1.31)
• Starsreplicate(stars,3)
• stars.namealpha centauri a, alpha centauri
  b,
• alpha centauri c
• Print, stars.name
• Print, stars0.name
• Note you dont need to name a structure type

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Miscellaneous

• gt? Gives you the help menu
• gt starts a comment line and is ignored by IDL
• - often helpful to comment copiously
• tells IDL to treat the next line as if it is
  part of the current
• line
• IDL is case and space insensitive. Unix is not!
• Most math operators work just the way youd think
  they do
• x53-16
• print, x