IDL Tutorial Day 1  Goals: 1 Introduce IDL basics 2 Describe fundamental IDL structures

IDL Tutorial Day 1 Goals: 1 Introduce IDL basics 2 Describe fundamental IDL structures PowerPoint PPT Presentation

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What is IDL?. 1970 IDL's predecessor, Laboratory for Atmospheric and Space Physics, CO1987 Unix environment1992 Widgets addedInteractive Data Language (IDL) is a programming language that is a popular data analysis language among scientists. It is has all of the program control opt

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IDL Tutorial Day 1 Goals: 1 Introduce IDL basics 2 Describe fundamental IDL structures

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1. IDL Tutorial Day 1 Goals: 1) Introduce IDL basics 2) Describe fundamental IDL structures Maria Kazachenko ([email protected])

2. What is IDL? 1970 – IDL’s predecessor, Laboratory for Atmospheric and Space Physics, CO 1987 – Unix environment 1992 – Widgets added Interactive Data Language (IDL) is a programming language that is a popular data analysis language among scientists. It is has all of the program control options of a standard programming language. Syntax includes many constructs from Fortran and some from C Many useful functions are available in large library Used by - NASA - Lockheed-Martin - Medical Imaging Fields

3. IDL under Unix

4. Basic Unix Commands >man command-name - looks at the manual page for the command >pwd - shows current working directory path >cd {dirname} - changes current directory into dirname >cd /home/ >chmod {options} - changes permission modes of a file >cp {filename}{path} - copies files from one directory/filename to another >cp f1 f2 - makes a file f2 identical to f1 >cp –r - copies a folder >emacs {filename} - runs the text editor named EMACS >find ./ -name ‘’t*’’ –print - searches the named directory and its sub- directories for files starting with ‘t’ >gv {} - X PostScript previewer >ls {directory} - shows directory listing >ls - prints the names of the files in the current directory >ls –l - shows long directory listing >mkdir dirname - makes a sub-directory named “dirname” in the current directory >ssh {machine-name} - secure alternative to telnet.

5. In this tutorial, IDL> refers to the IDL prompt. And > refers to OS prompt (outside IDL). Once in IDL, you type the stuff that comes after this. For example to enter the print command, I’ll have IDL>print,a and you would type in “print,a” at the command line. Also [brackets] in an IDL description indicate an optional item.

6. Starting IDL

7. Starting IDL In a terminal window, once an IDL “path” is setup (.idl_startup), type idl, idlde, sswidl, or sswidlde >sswidl sswidl calls IDL with solar software and specified paths which have useful programs for solar physics work. sswidlde calls a graphical developer, where sswidl simply works in your terminal window You’ll almost always use sswidl or sswidlde. To manually set the “paths” needed for your work, talk to your research advisor To use an OS command, enter $ prior to it (Exceptions: pwd, cd,’/disk…’) IDL>$ls ;lists content of current directory To exit out of IDL IDL>exit

8. Journal Procedure Records everything you enter, plus any error or processing messages output by IDL, into a text file IDL> journal,‘text_file’ ;opens the file & ;starts record IDL> command line IDL> journal ;closes the journal file To view, open journal file with any text editor > emacs text_file or > nedit text_file

9. General Strategies IDL> ? ; IDL help menu IDL> xdoc ; Sswidl (solar) help IDL> help, [variable, /str] ; Properties of variables IDL> z=fltarr(3,7) ; Defines new array (3x7) IDL> help,z ; Tells about z Z FLOAT = Array[3, 7] IDL> which,’’ ; Location of the program ; you’re using /disk/hl2/data/maria/projects/flares/LCT/ Unix text editors - nedit, emacs, pico, vi > nedit Don’t memorize all commands Keep notes on your work and use the IDL journal Write programs in steps Learn by doing - don’t be afraid to make mistakes!!!

10. Some basic syntax IDL is not case sensitive but Unix is IDL> help, var (=) IDL> HELP, Var IDL> journal, “text_file” (NOT =) journal, “Text_File” The up arrow key recalls the most recent IDL input lines Ctrl-e, Ctrl-a – moves cursor to the end, beginning of the line Ctrl-C – interrupts IDL-command IDL> ; comments out an IDL line Use & to enter more than one command on a line IDL> a=[1,2,3,4,5,6] & print,a,total(a) Commas separate arguments from one another IDL> plot,a,sin(a/5.)/exp(a/50.) ;plots function Use $ at the end of a line that needs to continue IDL> for i=0,5 do $ IDL> print,i,a[i] “All” programs end with .pro -

11. Basic Variable Types Integers - 1 byte – byte data type (0..256) IDL> a=bindgen(1) - 2 bytes – integers data type (0..2562-1) IDL> b=indgen(1) & print,5/3 1 - 4 bytes – long integers (0..2564-1) IDL> c=lindgen(1) - 8 bytes – 64-bit long integers (0..2568-1) Floating data types - 4 bytes – floats (exponent from-38 to 38) IDL>print,5./3. & y=float(3)/float(2) 1.66667 IDL> a=1.23456789 IDL> print,a,format=‘(f20.10)’ - 8 bytes – double-precision IDL> print,5d/3d 1.6666667 IDL> a=1.23456789d0 & print,a,format=‘(f20.10)’ IDL> xyouts,xloc,yloc,string(a,format=‘f(20.10)’) Strings (Text) IDL>x=‘Hi there!!!’

12. Assigning a Variable a Value, Algebra Variable_name = value - will automatically select a variable type IDL> a=5/3.+4.1 ; float 5.76667 Variable_name = function_name(argument) IDL> b=exp(a) 148.413 ; float 319.471 Variable_name = string(value) IDL> str=string(’10’) ; str=’10’ Variable_name = long(value), converts to long integer type. IDL>x=long(32000.0) ; long integer 32000 Variable_name = fix(value), convert to integer type. IDL> print,fix(!Pi) 3 ; integer Variable_name = float(value), convert into single precision float IDL> help,float(2) 2.00000 ;float Variable_name = double(value), converts into double precision float

13. Naming Variables Assign ‘readable’ variable names that make sense Variable names must start with a letter - NO: 6a=“gamma” OK: a6=“gamma” Variables should not have the same name as IDL functions -NO: plot=6.0 Variable names may not have spaces in them - NO: A 6=5 OK: A_6=5 Some characters are illegal or have special meanings - NO: a@=5, a.b=5 (used for structures), A+=5, A#=5

14. Organizational structures Scalars IDL> x=3. Vectors IDL> a=[0,1,2,3] & print,a[1] 1 Arrays (see IDL help for matrices) (index from zero) intarr(), fltarr(), dblarr(), strarr().indgen() IDL> q=intarr(2,2) 0 0 0 0 IDL> m=indgen(2,2) 0 1 2 3 IDL> print,m(0,1) 2 IDL> a=findgen(100,100) IDL> print,a[1,0] 1.00000 IDL> b=a[23:25,67:69] IDL> indx=where(a gt 10.) IDL> jndx=where(a[indx] le 100.) IDL> b=a[indx[ jndx]] makes b equal to 1-d array equal to the elements of a that are both larger than 10 and less than or equal to 100

15. Array operations Simple math operations (* by scalar, +, -); A 3-column by 2-row array: IDL> A = [ [0, 1, 2],[3, 4, 5] ,[5,6,7]] IDL>B=2*A 0 2 4 IDL>print,B 6 8 10 10 12 14 More complex math #, Multiply an array by another IDL> C=A#B N_elements: Total number of elements in array IDL> n=n_elements(A) Total(array): computes a sum of all elements Min(array): outputs the min value; also Max Minmax(array): outputs the min then max Rebin: Resize array IDL> C=Rebin(A,6,6) Eigenvec: finds eigenvectors

16. Structures Structures are variables that contain multiple variables (scalars, arrays, or other structures) Each variable contained within a structure is called a tag IDL> struct={[struct_name], tag_name1: tag_value1,…} Anonymous structure (may change tags) IDL> A={name:’alpha ori’, ra:5.33, dec:-7.6, red:fltarr(12)} IDL> help,/st NAME STRING 'alpha ori' RA FLOAT 5.44000 DEC FLOAT -7.60000 RED FLOAT Array[12] IDL> print,a.dec -7.6 IDL> a.dec=5.5 Named structure. Once a named structure is defined, you cannot change the names of the tags or the number of tags IDL> A={star, name:’alpha ori’, ra:5.33,dec:-7.6,red:fltarr(12)} Array of structures (see Help for replicate function) IDL> cataloga=replicate(a,585)

17. “Homework”

18. Questions

19. Loops Programs with vector and array expressions run faster than programs with scalars, loops, and IF statements. Consider the problem of adding all positive elements of array B to array A. IDL> FOR i = 0, (N-1) DO IF B[i] GT 0 THEN A[i] = A[i] + B[i] Or IDL> A = A + (B > 0) For…do – FOR statement is used to execute one or more statement repeatedly, while incrementing or decrementing a variable with each repetition. 1 1 IDL>FOR i = 1, 4 DO PRINT, i,i^2 2 4 3 9 4 16 Or if there are many lines in a loop, then write simple program PRO Test FOR i = 1, 4 DO BEGIN PRINT,i,i^2 ENDDO END

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