UVa ITC Research Computing Support Fall, 2002 Presented by the Research Computing Support Group Davi

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UVa ITC Research Computing SupportFall,
2002Presented by theResearch Computing Support
GroupDavid Drake, Kathy Gerber, Ed Hall,
Tim F. Jost Tolson

• Overview of Research Hardware, Software, Support
  Storage Tuesday, September 10, 330 PM
• Statistical Software Thursday, September 12,
  330 PM
• Mathematical Visualization Software Tuesday,
  September 17, 330 PM
• High Performance Computing Thursday, September
  19, 330 PM
• FEMLAB Seminar Multiphysics Modeling Friday,
  Sept. 27 at 1000 AM
• Introduction to IDL Wednesday, October 9 at
  Noon
• Databases and the Web Wednesday, October 23 at
  3 pm
• Maple 8 Wednesday, November 20 at 3 pm

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Introduction to IDL

• By David Drake
• Research Computing Support Center
• Phone [phone] Fax [phone]

• E-Mail Res-Consult_at_Virginia.EDU
• http//www.itc.Virginia.edu/researchers

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Outline

• Introduction (What is IDL?)
• The IDL Development Environment (IDLDE)
• Documentation
• Programming
• Advanced Topics
• Examples Other Resources

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I. Introduction

• IDL Interactive Data Language
• Got started as a language for handling and
  processing images
• UVas IDL webpage (http//www.itc.virginia.edu/res
  earch/idl/)

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Key Features Highlights

• Rapid application development with GUI
  development environment
• Support for numerous file formats
• Image BMP, GEO TIFF, Interfile, JPEG, NRIF,
  PICT, PNG, PPM, SRF, TIFF, X11 Bitmap, XWD
• Scientific CDF, HDF, HDF-EOS, netCDF
• Other ASCII, Binary, DICOM, DXF, WAV, XDR

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More Features Highlights

• Plotting data visualization
• 2D, 3D, volume, surface, contour, mapping
• Irregular grids
• Animation
• Signal image processing
• GUIBuilder application interface development tool

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Still More Features

• Multithreading with multiple CPU support
• Inter-language communication (Fortran C)
• External calls from IDL
• Extending IDL with built-in routines
• Calling IDL from external applications
• Talk to IMSL libraries

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II. The IDLDE

• Starting the IDLDE
• Windows Start Programs IDL 5.5 IDL
• Macintosh (currently requires a HASP)
• Unix
• idlde (or idl to invoke only the command line
  interface)
• For IDL files, look in /common/rsi/idl_5.5

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The IDLDE Window
Menu bar
Tool bars
Multiple Document Panel
Project Window
Output Log
Variable watch window
Command line
Status bar
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Setting Preferences

• Graphics To make the graphics output work
  correctly on most systems, first thing to do is
  to enter
• DEVICE, RETAIN2, DECOMPOSED0
• at the beginning of each session. This is the
  best option for cross-platform work. The
  RETAIN2 option forces IDL to buffer IDL windows
  that become covered. The DECOMPOSED0 setting
  allows users with DirectColor and TrueColor
  displays to use IDL programs written for
  standard, PseudoColor (8 bit 256 color)
  displays without modification.

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More Preferences

• The Startup file (startup.pro) DEVICE statement
  above can be included in an IDL startup file
  called startup.pro and run each time IDL is
  started. Set this option in File Preferences
  Startup.
• Path For ease of use, add your working directory
  to your IDL path. Set this option in File
  Preferences Path

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III. Documentation

• RSI Online Manuals (pdf) located in
• Windows (C\Program Files\RSI)\IDL 5.5\docs
• Unix /common/rsi/idl_5.5/docs
• Macintosh RSIIDL 5.5docs
• Start with Getting Started
• Note that documents (both pdfs help menu) are
  really for version 5.4, so
• Take a look at Whats New in IDL 5.5 Whats New
  in IDL 5.4

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Be Aware of

• Using IDL
• Building IDL Applications
• IDL Reference Guide
• External Development Guide
• Scientific Data Formats
• IDL Wavelet Toolkit Users Guide
• IDL Quick Reference

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IV. Programming

• IDL syntax is case-insensitive (except for unix
  filenames directory structures, etc.)
• Special characters (Help Contents Contents
  IDL Reference Special Characters)
• begin comment (to end of line)
• line continuation
• separate two commands on same line
• _at_ execute (following) batch file
• end label identifiers

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Statements

• Normal assortment (Help Contents Contents
  IDL Reference Functional List of Routines
  Statements)
• begin end
• if then case endcase switch
• for repeat until while do
• break continue goto
• pro function see below
• common

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Command Line Entries

• Statements are (compiled and) executed
  immediately, and in this sense, IDL is an
  interpretive language
• Multiple statements on a single line must be
  separated by an ampersand ()
• Each command (e.g. for loops) must be fully
  contained on one effective line
• Concatenate using or
• Multi-lined commands must be continued using
  at the end of the line

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Command Line Examples

• Command concatenation
• j 0 for i 1,10 do j j 1
• Line continuation
• for i 1,10 do begin j j i k k i
  endfor

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Command Line Journaling

• Command line entries can be saved to a journal
  file.
• To start the journal (which overwrites any
  existing file) enter
• JOURNAL, filename
• To stop journaling, enter
• JOURNAL

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Batch Commands

• Batch files are run by entering _at_filename at
  the command line, e.g.
• _at_C\IDLbatch\mybatch.xyz
• Can be advantageous for code development in that
  batch variables remain available for manipulation

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Procedures

• Self-contained code unit with a unique name that
  is called by other code units to perform a
  desired duty
• The calling code and procedure communicate via
  passed arguments
• Must start with PRO procedure name and end with
  an END statement
• Must be compiled

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Procedure Example

• DefinedPRO add, A, B, Boolean Bool END
• Called
• Add, 4, 7, /Boolean BA4, B7, Bool1
• Add, Bo 5 shortest, unambiguous abbreviation
  OK
• Add, 5 Only A is defined B, T undefined

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Functions

• Similar to procedures except that they return a
  value, and so can be used in expressions The
  calling code and procedure communicate via passed
  arguments
• Must start with FUNCTION function name and end
  with an END statement
• Must be compiled

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Function Example

• DefinedFunction add, A, B, TESTT if
  n_elements(A) eq 0 then A 0 if n_elements(B)
  eq 0 then B 0 if T5 then RETURN AB else
  RETURN A B END
• Called
• C Add, 4, 7, TEST 5 C 28
• D add, 3, TE 5 D 3 B is not defined
• E add 5 E 5 only A is defined

Allows testingof parameters
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Vectorization

• Array processing
• Much faster than looping
• Use IDL array operations whenever possible
• Avoid loops
• Avoid if statements
• Example _at_Array_vs_Loop.b

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Debugging Profiling

• Standard Debugging Tools
• Access from the Run menu, from hotkeys, or from
  buttons
• Step Into Over Out
• Trace
• Run to Cursor Return
• Set Disable Edit Breakpoints
• Built-in Profiler
• Profile selected user and/or system modules

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Graphics Modes

• Direct
• Graphics are sent directly to devices (e.g. X for
  X-windows displays, WIN for Windows displays, PS
  for PostScript files, etc.), which are set using
  the SET_PLOT command.
• Once a direct-mode graphic is drawn to a graphics
  device, it cannot be altered or re-used. To
  re-create a graphic on another device, the IDL
  commands must be re-issued to that device.
• Graphics added to a device are drawn in front of
  existing graphics.

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Graphics Modes (cont.)

• Object
• Objects are self-contained entities and are
  designed for building interactive
  three-dimensional visualization applications.
  They are not designed (or meant to be designed)
  to interact with system variables or other
  external structures.
• Objects are persistent and take up more system
  resources including memory. Programmers should
  be especially cognizant of memory issues and
  memory leaks.

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V. Advanced Topics

• Object Oriented Programming (Building IDL
  Applications, Part IV Using IDL Objects Help
  Contents Contents Building IDL Applications
  Using IDL Objects)
• Creating GUIs (Building IDL Applications, Part
  V Creating GUIs Help Contents Contents
  Building IDL Applications Using the IDL GUI
  Builder)
• Multiprocessor/Multithreading support (Whats New
  in IDL 5.5)
• External dynamic linking
• Making use of IMSL libraries
• Calling IDL from FORTRAN C programs

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VI. Examples

• Plots
• Some batch files enter _at_filename at the command
  line
• _at_SalmonPlot.b, _at_Plot2axes.b, _at_FilledContour.b,
  _at_CircleColorPlot.b (needs circle.pro),
  _at_SurfaceContour.b _at_GaussContour.b, _at_Bessel.b
• Printing
• _at_SalmonPrint.b
• FileIO, pointers, 3-d visualization
• _at_HeadImport.b (needs Head Import.tf),
  RandomVolume.b, xplot.pro (needs xplot.zip)

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More Examples

• IDL Demo
• Source code in idl55\examples\demo\demosrc
  directory
• Other IDL examples
• Look in idl55\examples\visual
• IDLs user contribution library
• Other resources
• See David Fannings webpages and especially his
  coyote files
• e.g. texture_surface.pro

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Other Resources

• IDL Webinars (web seminars)
• Available from RSI (login account required)
• Topics include
• Introduction to IDL
• Importing Raw Binary Data Basic Display in IDL
• IDL HDF5 Support
• IDL GUI Builder
• IDL Programming Techniques (1st edition)
• Available for browsing from the RCSC