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Introduction to IDL Functions and Procedures: Day 2 Overview with Michael Hahn

In this second day of the IDL tutorial, Michael Hahn delves into utilizing pre-written functions and procedures. The session highlights essential topics such as plotting, Xdoc usage, writing macros, and the concepts of procedures and functions. Key functions like `size`, `sin`, `plot`, and `restore` are discussed, providing practical examples on their application. Attendees will learn how to effectively search for and use routines via Xdoc, streamline programming with macros, and save/restore variables, making this session ideal for anyone looking to enhance their IDL programming skills.

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Introduction to IDL Functions and Procedures: Day 2 Overview with Michael Hahn

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  1. IDL Tutorial: Day 2 Michael Hahn (hahn@solar.physics.montana.edu)

  2. Today’s Topics • Using Functions and Procedures already written - e.g. plotting • Xdoc • Writing Scripts (Macros) • Save and Restore • Structures

  3. Functions and Procedures • Two basic types of programs • Functions: result=function_name(parameter, Keyword=Set, …) Examples: size, n_elements, sin, cos, reverse, where - Functions can be placed anywhere you can put a value • Procedures: procedure_name, param1, param2, Keyword=Set… Examples: help, print, open, printf, plot, set_plot, device, save - Procedures do stuff, but don’t 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

  4. xdoc • Xdoc allows you to graphically brose the lbirary of Solarsoft routines • Type in xdoc at IDL command prompt • Can search for the name of a procedure/function • Usually you don’t know the name, xdoc makes it ‘easy’ for you to search for it

  5. Commonly Used Procedures • print: for printing stuff (to screen) e.g. > print, sin(x) • plot: plot variables to the current graphics device (usually screen) > plot, x, sin(x), Title=“sin Plot”, xtitle=“x”, $ ytitle=“sine of x” • set_plot: tells idl where to send plots to. Screen (Xdisplay) is default - set_plot,”x” ;sends output to the x display - set_plot, “ps”; sends the output to a postscript file with default name idl.ps. Read ps files with ghostview unix_prompt> gv idl.ps • device: changes properties of the device currently enabled by set_plot. See help menu.

  6. Commonly Used Functions • Many math operators are functions > y=sin(x) > y=cos(x) >y=exp(x); exponential function • Where allows you to pick out the index of an array that meets some criterion > index=where(new_array eq 15) (more on boolean operators later) • Replicate makes copies of variables, arrays, structures, etc... > stars=replicate(stars,15) • dialog_pickfile allows you to graphically pick out file names > file_name=dialog_pickfile()

  7. 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: > .run program_name > .rnew program_name

  8. 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: save, variable1, variable1, file=‘file.sav’ • Restore allows you to restore saved variables to a session Example: restore, ‘file.sav’

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