IDL_Intro

8/2/2019 IDL_Intro

1/61

Introduction to IDL

Thayer School of EngineeringSimon Shepherd

[email protected]://thayer.dartmouth.edu/~simon

A Kiewit Minicourse

8/2/2019 IDL_Intro

2/61

Minicourse: Introduction to IDL February 2005

IDL

AgendaWhat is IDL ?How to run IDL

Simple IDL CommandsArrays in IDL

Data I/OBasic PlottingBuilt-in Analysis FunctionsMapping

Example

8/2/2019 IDL_Intro

3/61


IDL

Scientific Computing Today

Numeric/graphics: IDL, Matlab, Octave

Symbolic: Maple, Mathematica, MathCad

Dataflow: LabView, Simulink, AVS, DX, OpenDX

Scripting languages: sh, csh, bash, Tcl, Perl

Traditional programming languages:Basic, Pascal, FORTRAN, C, C++, Java

8/2/2019 IDL_Intro

4/61


IDL

What is IDL ?Interactive D ata L anguage

8/2/2019 IDL_Intro

5/61


IDL


Proprietary software distributed by Research S ystems, Inc. ofBoulder, CO now a division of Kodak.

8/2/2019 IDL_Intro

6/61


IDL



Grew out of programs written for analysis of data from NASA missions such as Mariner and the International Ultraviolet Explorer.

8/2/2019 IDL_Intro

7/61Minicourse: Introduction to IDL February 2005

IDL




Oriented toward use by scientists and engineers in the analysis and visualization of multi-dimensional data sets.

8/2/2019 IDL_Intro


IDL


Platform Independent: Unix, linux, Windows, Macintosh



Oriented toward use by scientists and engineers in the analysis and visualization of multi-dimensional data sets.

8/2/2019 IDL_Intro


IDL


Offers all the power , adaptability , and programmability ofhigh level languages like FORTRAN, C, and C++.

8/2/2019 IDL_Intro


IDL


Offers all the power , adaptability , and programmability ofhigh level languages like FORTRAN, C, and C++.

But it adds two capabilities which are essential for moderndata analysis: interactivity and graphics display.

8/2/2019 IDL_Intro

11/61

8/2/2019 IDL_Intro


IDL

Ways to Run IDL

Interactively

Batch mode

Development Environment ( DE)

Command Line

8/2/2019 IDL_Intro


IDL

Ways to Run IDL

Batch mode

prompt> idl filename

where filename contains a list of IDL commands

commands are interpreted as if they were entered

at the command lineNo multiline statements such as

begin...end

8/2/2019 IDL_Intro


IDL

Ways to Run IDL

Command Line

prompt> idl

each command entered is interpreted and executedand the prompt is returned

IDL> command

IDL>

8/2/2019 IDL_Intro

15/61

8/2/2019 IDL_Intro

16/61


IDL Graphical User Interface (DE)

8/2/2019 IDL_Intro

17/61


IDL

menu

Graphical User Interface (DE)

8/2/2019 IDL_Intro

18/61


IDL

toolbar


8/2/2019 IDL_Intro

19/61

8/2/2019 IDL_Intro

20/61


IDL

project


8/2/2019 IDL_Intro

21/61


IDL

output


8/2/2019 IDL_Intro

22/61


IDL

variables


8/2/2019 IDL_Intro

23/61


IDL

command line


8/2/2019 IDL_Intro

24/61


IDL

Using IDL as a calculatorIDL> a = 3 ; assignment statement

; semicolon is used for comments

IDL> print , a + 4 ; built-in print command7

IDL> print , a + 4. ; variables dynamically typed7.00000 ; take on highest precision

IDL> print , a + 4D; double precision

7.0000000IDL> print , a * 1e-9 ; scientific notation

3.00000e-09

Note: variable names are case insensitive ( A = a )

8/2/2019 IDL_Intro

25/61


IDL

Data Types1 Byte n B 8-bit unsigned

2 Integer n 16-bit signed

3 Longword n L 32-bit signed

4 Floating Point n.n 32-bit (+10 38 )

5 Double-Precision n.n D 64-bit (+10 38 )

6 Complex COMPLEX (n.n,n.n ) real/imaginary pairs7 String 'ssss' 0-32k in length

8 Struct User-defined Structure

9 D-P Complex DCOMPLEX (n.n,n.n ) real/imaginary pairs double-precision

10 Pointer Pointer

11 ObjRef Object Reference12 Unsigned Int n U 16-bit unsigned

13 Unsigned Long n UL 32-bit unsigned

14 64-bit Long LONG64 (n ) 64-bit signed longword

15 64-bit Unsigned Long ULONG64 (n ) 64-bit unsigned longword

8/2/2019 IDL_Intro

26/61


IDL

Unary and Compound OperatorsIDL> a = 3 ; assignment statement

IDL> a += 5 ; C compound operatorsIDL> a = a + 5 ; equivalent but rather tedious

IDL> print , a-- ; careful...8

IDL> print , a8

IDL> a++ ; C unary operatorsIDL> print , a

8

IDL> print , a7

8/2/2019 IDL_Intro

27/61


IDL

Arrays in IDL

Dynamically sized (and resized)

Any data type (but not mixed)

Array-oriented language

operations are performed on arrays

8/2/2019 IDL_Intro

28/61


IDL

Vectors in IDLIDL> vec = [ 3 , 5 , 1 , 4 , 5] ; assignment statement

IDL> print , vec ; 5 element vector 3 5 1 4 5

IDL> print , vec[ 3] ; elements of array 9

vec[ 0] vec[ 1] vec[ 2] vec[ 3] vec[ 4]

IDL> vec[ 3] = 9 ; square brackets to access

8/2/2019 IDL_Intro

29/61

8/2/2019 IDL_Intro

30/61


IDL

Matrices in IDLIDL> print , mat[ 3, 1] ; access elements of matrix

9

column row

IDL> print , mat[ 5*1+3] ; equivalent...9

column row format... M

M by N

M

8/2/2019 IDL_Intro

31/61


IDL

Matrices in IDL

; n th row: n*M m th column: m

1*5 + 3 = 8

3 5 1 4 5

8 3 2 9 1

column 0 1 2 3 4row

0

1

M by N

5 by 2

mat[ 3, 1] = mat[ 5*1+3]

8/2/2019 IDL_Intro

32/61


IDL

Declaring MatricesIDL> mat = [[ 3 , 5 , 1 , 4 , 5],[ 8 , 3 , 2 , 9 , 1]] ; explicitlyIDL> mat = fltarr ( 5, 2) ; all zeros

IDL> arr = dblarr ( 8, 5 , 2) ; other types

P by M by N array

arr[ 6 , 2 , 1] = arr[n*P*M + m*P + p]

40 + 16 + 6

8/2/2019 IDL_Intro

33/61

8/2/2019 IDL_Intro

34/61

8/2/2019 IDL_Intro

35/61


IDL

Searching ArraysIDL> mat = [[ 3 , 5 , 1, 4 , 5],[ 8 , 3 , 2, 9 , 1]] ; 5 by 2

IDL> q = where (mat le 2 , nq) ; find all elements; in mat that are print , q ; indices of the array2 7 9

IDL> print , mat[q] ; values of the array1 2 1

IDL> print , nq ; optional, but good3 ; to check...

also: eq , ge , gt , lt

8/2/2019 IDL_Intro

36/61


IDL

Array SizeIDL> mat = [[ 3 , 5 , 1, 4 , 5],[ 8 , 3 , 2, 9 , 1]] ; 5 by 2

IDL> print , n_elements (mat[ 0,*]) ; vector2

IDL> print , n_elements (mat) ; total number for10 ; multi-dimensional

IDL> print , size (mat) ; more information2 5 2 2 10

# dimensions

elements inx dimension

1 st 2nd data type total elements

8/2/2019 IDL_Intro

37/61


IDL

Array Calculations

IDL> x = findgen (n+ 1)* 2*!pi /n ; x = [0,2 ] in; steps of 2 /100

IDL> n = 100 ; declare num

IDL> y = cos (x) ; element-by-element; assignment

Note: !pi is a system variable

No looping necessarycleaner looking codefaster execution

IDL> y = print , y[ 0: 5]1.00000 0.998027 0.992115 0.982287 0.968583 0.951057

Also: system structures such as !p , !x , !y , etc.e.g. !p.multi = [ 0, ncol , nrow , nz , order ]

8/2/2019 IDL_Intro

38/61


IDL

Array CalculationsUsing C

#define N 101int n;

float pi= 3.1415926 ;float x[N], y[N];

dx = 2*pi/N;for (n= 0;n

8/2/2019 IDL_Intro

39/61


IDL

Array CalculationsUsing C

#define N 101int n;

float pi= 3.1415926 ;float x[N], y[N];

dx = 2*pi/N;for (n= 0;n

8/2/2019 IDL_Intro

40/61

8/2/2019 IDL_Intro

41/61

8/2/2019 IDL_Intro

42/61


IDL

Executive Commands

file loop.pro

n = 101dx = 2*!pi /nfor i= 0,n- 1 do begin

x[n] = n*dxy[n] = cos (x[n])

endforend

IDL> .run loop.proIDL>

to execute commands in loop.pro

Other executive commands: (can only be used at the IDL command line ).compile , .edit ,.run , .go , .continue , .out , .return , .run , .skip , .step , .stepover , .trace

(or Dot Commands)

8/2/2019 IDL_Intro

43/61


IDL

Reading/Writing Files in IDL

Read in data from file:

openr , readf

Interactively with the DE

Write data to a file:

openw , writef

8/2/2019 IDL_Intro

44/61


IDL

Reading Data from a FileIDL> filename = 'ssn.dat' ; declare filenameIDL> nlines = 3072 ; cheat...IDL> record = {time: 0.0 , ssn: 0.0 } ; declare structIDL> data = replicate (record, nlines) ; make array of structsIDL> openr , ifile, filename, /get_lun ; open file for readIDL> readf , ifile, data ; read block of dataIDL> free_lun , ifile ; clean up...IDL> print , data[ 0: 9]. time ; access range of data

1749.05 1749.13 1749.21 1749.29 1749.38 1749.461749.54 1749.63 1749.71 1749.80

Note: must know number of lines ...can do with spawn , 'wc -l ' +filename

or by looping while not eof (ifile) do beginreadf , ifile, record

data[i++] = record

endwhile

8/2/2019 IDL_Intro

45/61


IDL

Interactively with the DE

Reading Data from a File

8/2/2019 IDL_Intro

46/61

8/2/2019 IDL_Intro

47/61


IDL

Plotting Features in IDL

IDL has built-in 2D and 3D plotting capabilities

plot , [X,] Y [, /ISOTROPIC ][, /XLOG][, /YLOG]

IDL> plot , data.time , data.ssn

IDL

8/2/2019 IDL_Intro

48/61


IDL

Plotting Features in IDL

Many options for making fancier plots...

IDL> plot , data.time , data.ssn , $

xrange= [ 1980 , 2005 ], xtitle= 'Year' , $ytitle= 'Monthly Observed Sun Spot Number'

IDL

8/2/2019 IDL_Intro

49/61


IDL

IDL> sm_data = smooth (data.ssn, 6)

IDL> oplot , data.time , sm_data, $

color= 200 , thick= 4

; smooth the data with a 6 point (month); boxcar average

; overplot the smoothed data in a; different color and thicker line

IDL> loadct , 39

Plottin g Features in IDL

IDL

8/2/2019 IDL_Intro

50/61


IDL

Spectral Analysis

IDL> H = fft ( data.ssn ) ; use the built-in fftIDL> ndat = n_elements (data.ssn ) ; number of data pointsIDL> q = indgen (ndat/ 2- 1)+ 1 ; negative frequenciesIDL> p = ndat - q ; positive frequencie s

IDL> PSD = fltarr (ndat/ 2+1) ; declare PSD holderIDL> PSD[ 0] = abs (H[ 0])^ 2 ; load theIDL> PSD[q] = abs (H[q])^ 2abs (H[p])^ 2 ;IDL> PSD[ndat/2] = abs (H[ndat/2])^ 2 ;

IDL> per = ndat * 1. / 12 / findgen (ndat/ 2+1) ; in years

IDL> plot , per, PSD, xrange= [ 0, 20 ], /nodata , ; init plotxtitle= 'Period (years)'

IDL> oplot , per, PSD, color= 250 , thick=2 ; plot PSD

Estimate the power spectrum (see Numerical Recipes )

IDL

8/2/2019 IDL_Intro

51/61


IDL

Correlation Analysis

Discrete Math Functions

Curve and Surface Fitting

Differentiation and Integration

Eigenvalues and EigenvectorsGridding and Interpolation

Optimization

Linear Systems including LAPACK Routines

Nonlinear Equations

Statistics and Probability

Multivariate Analysis

IDL M C li d Pl

8/2/2019 IDL_Intro

52/61


IDL More Complicated Plots

8/2/2019 IDL_Intro

53/61

8/2/2019 IDL_Intro

54/61

8/2/2019 IDL_Intro

55/61

IDL

8/2/2019 IDL_Intro

56/61


IDL

Mapping Features in IDLIDL> map_set , 70 , -75 , /orthographic , /grid , $IDL> /continent , /noborder, $IDL> e_continents= {fill: 1 , color: 150 }, $IDL> e_horizon= {fill: 1 , color: 50 }

orthographic map projection

rotated view

colored

8/2/2019 IDL_Intro

57/61

IDL

8/2/2019 IDL_Intro

58/61


IDL

Data on Maps

8/2/2019 IDL_Intro

59/61

8/2/2019 IDL_Intro

60/61

8/2/2019 IDL_Intro

61/61

IDL_Intro

Documents

Transcript of IDL_Intro