1 / 24

M AT L AB

Learn about the MATLAB user environment, including the workspace/variable inspector, command window, command history, and ways to get help. Get familiar with setting paths and configuring your MATLAB environment.

paulasalgado
Download Presentation

M AT L AB

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. MATLAB Basics

  2. MATLAB User Environment Workspace/Variable Inspector Command Window Command History

  3. Getting help There are several ways of getting help: Basic help on named commands/functions is echoed to the command window by: >> help command-name A complete help system containing full text of manuals is started by: >> helpdesk

  4. System Environment • Windows • MATLAB installed in c:\matlab6.5 • Your code…anywhere convenient (e.g. h:\matlab) • Linux (Environment network) • MATLAB installed in /apps/matlab • Your code in /home/username/matlab • Your environment configuration in ~/.matlab

  5. startup.m • The script $matlab_root\toolbox\local\matlabrc.m is always run at startup – it reads system environment variables etc, and initialises platform dependent settings. If present it will run a user defined initialisation script: startup.m • Linux: /home/user/matlab/startup.m • Windows: $matlab_root\toolbox\local\startup.m • Use startup.m for setting paths, forcing preferred settings, etc.

  6. Example startup.m file (for my laptop) %------------------------------------- % Matlab startup file for IMB's laptop %------------------------------------- %-- add paths for my m-files -- addpath d:/matlab addpath d:/matlab/bulk2.5 addpath d:/matlab/bulk2.6 addpath d:/matlab/coastal addpath d:/matlab/lidar addpath d:/matlab/ndbc addpath d:/matlab/page addpath d:/matlab/sections addpath d:/matlab/sharem addpath d:/matlab/wavelet addpath d:/matlab/LEM addpath d:/matlab/GPSbook addpath d:/matlab/FAAM addpath d:/matlab/FAAM/winds addpath d:/matlab/faam/bae %-- add netCDF toolbox -- addpath c:/matlab701/bin addpath c:/matlab701/bin/win32 addpath d:/matlab/netcdf addpath d:/matlab/netcdf/ncfiles addpath d:/matlab/netcdf/nctype addpath d:/matlab/netcdf/ncutility %-- add path for generic data -- addpath d:/matlab/coastlines % coastline data addpath d:/cw96/flight_data/jun02 % raw cw96 addpath d:/cw96/flight_data/jun07 % aircraft data addpath d:/cw96/flight_data/jun11 addpath d:/cw96/flight_data/jun12 addpath d:/cw96/flight_data/jun17 addpath d:/cw96/flight_data/jun19 addpath d:/cw96/flight_data/jun21 addpath d:/cw96/flight_data/jun23 addpath d:/cw96/flight_data/jun26 addpath d:/cw96/flight_data/jun29 addpath d:/cw96/flight_data/jul01 addpath d:/cw96/runs % run definitions for cw96 flights %---------------------------------------------------------------------- %-- set default figure options -- set(0,'DefaultFigurePaperType','a4') % this should be the default in EU anyway set(0,'DefaultFigurePaperUnits','inches') % v6 defaults to cm for EU countries set(0,'DefaultFigureRenderer','painters') % v7 default OpenGL causes problems

  7. addpath – adds directories to the search path. MATLAB will look in ALL directories on the path for: Functions and scripts (.m files) MATLAB data files (.mat files) It will also look in the current directory The ‘set’ commands in the example startup.m file set some default graphics properties, overriding the defaults – will cover these later.

  8. The WORKSPACE • MATLAB maintains an active workspace, any variables (data) loaded or defined here are always available. • Some commands to examine workspace, move around, etc: who : lists variables in workspace >> who Your variables are: x y

  9. whos : lists names and basic properties of variables in the workspace >> whos Name Size Bytes Class x 3x1 24 double array y 3x2 48 double array Grand total is 9 elements using 72 bytes pwd, cd, dir, ls : similar to operating system (but no option switches) >> pwd ans = D:\ >> cd cw96\jun02 >> dir . 30m_wtv.mat edson2km.mat jun02_30m_runs.mat .. 960602_sst.mat edson_2km_bulk.mat

  10. VARIABLES • Everything (almost) is treated as a double-precision floating point array by default • Typed variables (integer, float, char,…) are supported, but usually used only for specific applications. Not all operations are supported for all typed variables. • [IDL uses typed variables, but allows mixing of types...at least to some extent]

  11. >> x=[1 2 3] x = 1 2 3 >> x=[1,2,3] x = 1 2 3 >> x=[1 2 3 4]; >> x=[1;2;3;4] x = 1 2 3 4 When defining variables, a space or comma separates elements on a row. A newline or semicolon forces a new row; these 2 statements are equivalent. NB. you can break definitions across multiple lines.

  12. 1 & 2D arrays are treated as formal matrices • Matrix algebra works by default: 1x2 row oriented array (vector)(Trailing semicolon suppresses display of output) >> a=[1 2]; >> b=[3 4]; >> a*b ans = 11 >> b*a ans = 3 6 4 8 2x1 column oriented array Result of matrix multiplication depends on order of terms (non-cummutative)

  13. Element-by-element operation is forced by preceding operator with ‘.’ >> a=[1 2]; >> b=[3 4]; >> a.*b ??? Error using ==> times Matrix dimensions must agree. Size and shape must match

  14. >> a=[1 2] A = 1 2 >> b=[3 4]; >> a.*b ans = 3 8 >> c=a+b c = 4 6 No trailing semicolon, immediate display of result Element-by-element multiplication Matrix addition & subtraction operate element-by-element anyway. Dimensions of matrix must still match!

  15. >> A = [1:3;4:6;7:9] A = 1 2 3 4 5 6 7 8 9 >> mean(A) ans = 4 5 6 >> sum(A) ans = 12 15 18 Most common functions operate on columns by default

  16. MATLAB indexes arrays: 1 to N [row,column] [1,1 1,2 . 1,n 2,1 2,2 . 2,n 3,1 3,2 . 3,n . . . m,1 m,2 . m,n] IDL indexes arrays: 0 to N-1 [column,row] [0,0 1,0 . n-1,0 0,1 1,1 . n-1,1 0,2 1,2 . n-1,2 . . . . 0,m-1 1,m-1 . n-1,m-1] INDEXING ARRAYS n m

  17. >> A = [1:3;4:6;7:9] A = 1 2 3 4 5 6 7 8 9 >> A(2,3) ans = 6 >> A(1:3,2) ans = 2 5 8 >> A(2,:) ans = 4 5 6 The colon indicates a range, a:b (a to b) A colon on its own indicates ALL values

  18. THE COLON OPERATOR • Colon operator occurs in several forms • To indicate a range (as above) • To indicate a range with non-unit increment >> N = 5:10:35 N = 5 15 25 35 >> P = [1:3; 30:-10:10] P = 1 2 3 30 20 10

  19. To extract ALL the elements of an array (extracts everything to a single column vector) >> A = [1:3; 10:10:30; 100:100:300] A = 1 2 3 10 20 30 100 200 300 >> A(:) ans = 1 10 100 2 20 200 3 30 300

  20. LOGICAL INDEXING • Instead of indexing arrays directly, a logical mask can be used – an array of same size, but consisting of 1s and 0s – usually derived as result of a logical expression. >> X = [1:10] X = 1 2 3 4 5 6 7 8 9 10 >> ii = X>6 ii = 0 0 0 0 0 0 1 1 1 1 >> X(ii) ans = 7 8 9 10

  21. Basic Operators +, -, *, / : basic numeric operators \ : left division (matrix division) ^ : raise to power ’ : transpose (of matrix) – flip along diagonal • fliplr(), flipud() : flip matrix about vertical and horizontal axes.

  22. SAVING DATA • MATLAB uses its own platform independent file format for saving data – files have a .mat extension • The ‘save’ command saves variables from the workspace to a named file (or matlab.mat if no filename given) • save filename – saves entire workspace to filename.mat • save var1 var2 … filename – saves named variables to filename.mat • By default save overwrites an existing file of the same name, the –append switch forces appending data to an existing file (but variables of same name will be overwritten!) • save var1 var2 filename -append

  23. Data is recovered with the ‘load’ command • load filename – loads entire .mat file • load filenamevar1 var2 …– loads named variables • load filename –ascii – loads contents of an ascii flatfile in a variable ‘filename’. The ascii file must contain a rectangular array of numbers so that it loads into a single matrix. • X=load(‘filename’,’-ascii’) – loads the ascii file into a variable ‘X’ • save var1 filename –ascii – saves a single variable to an ascii flat file (rectangular array of numbers)

  24. There have been changes to the internal format of .mat files between MATLAB v4 and v5 (major changes to allow arrays with more than 2 dimensions, structures, cell arrays…), and again with v7 (minor change to use unicode instead of ascii).Later versions will load old format files. You can force save to an old file format with –v4 and –v6 switchessave filename –v6

More Related