MATLAB Second Seminar

Transcription

1 MATLAB Second Seminar

2 Previous lesson Last lesson We learnt how to: Interact with MATLAB in the MATLAB command window by typing commands at the command prompt. Define and use variables. Plot graphs It would be nice if you didn't have to manually type these commands at the command prompt whenever you want to use them.

3 Script M-filesM Standard ASCII text files Contain a series of MATLAB expressions A script does not define a new workspace % Comments start start with with "%" "%" character pause pause % Suspend execution - hit hit any any key key to to continue. keyboard % Pause Pause & return control to to command line. line. % Type Type "return" to to continue. break break % Terminate execution of of current loop/file. return % Exit Exit current function % Return to to invoking function/command line. line. Continue % go go to to next next iteration Input Input % Prompt for for user user input input

4 Creating Scripts with MATLAB Editor/Debugger Automatically just saves files as ASCII text files for you. Scripts in MATLAB has the ".m" suffix. They are also called "M-files". Open Matlab Editor: File New M-file OR: >> edit Run

5 A Simple Script Write a program which receives a number from the user, calculates it s square root (use sqrt command) and after the user hits a key, displays the result. save the script as "square_root_script.m" % a simple MATLAB m-file to calculate the % square root of an input numbers. my_num=input('insert a number'); % now calculate the square root of the number and print it out: square_root = sqrt(my_num); disp ('Hit any key to see the result') pause; square_root

6 Running Scripts >> square_root_script The header - comments you place at the beginning of your scripts will be returned to users when they get help for your script. >> help square_root_script Note: The variables defined in the script remain in the workspace even after the script finishes running,

7 Running Scripts (2) Find and Replace ctrl+f Key words Wrong use of key words Indenting: Ctrl+I

8 Flow Control Constructs Logic Control: IF / ELSEIF / ELSE SWITCH / CASE / OTHERWISE Iterative Loops: FOR WHILE

9 The if, elseif and else statements Works on Conditional statements Logic condition is true if its different then 0. if if I == == J A(I,J) = 2; 2; else else if if abs(i-j) == == 1 A(I,J) = -1; -1; else else A(I,J) = 0; 0; end end %else %else if if end end %if %if if if I == == J A(I,J) = 2; 2; elseif abs(i-j) == == 1 A(I,J) = -1; -1; else else A(I,J) = 0; 0; end end ELSEIF does not need a matching END, while ELSE IF does.

10 Switch, Case, and Otherwise More efficient than elseif statements Only the first matching case is executed switch input_num case case -1-1 input_str = 'minus one'; one'; case case 0 input_str = 'zero'; case case 1 input_str = 'plus 'plus one'; one'; case case {-10,10} input_str = '+/- '+/- ten'; ten'; otherwise input_str = 'other value'; end end

11 Problem Build a program which receives a variable x and its units (mm, cm, inch, meter) and calculates Y- it s value in centimeters units. Use switch case. 1 Inch = 2.54 cm Write a comment for error case. Save the file under units.m

12 Solution x = 3.0; 3.0; units units = 'mm'; 'mm'; switch units units case case {'in','inch'} y = 2.54*x; % converts to to centimeters case case {'m','meter'} y = x*100; % converts to to centimeters case case { 'millimeter','mm'} y = x/10; x/10; disp disp ([num2str(x) ' in in ' units units ' converted to to cm cm is is :' :' num2str(y)]) case case {'cm','centimeter'} y = x; x; otherwise disp disp (['unknown units:' units]) y = nan; nan; end end

13 The for loop Similar to other programming languages Repeats loop a set number of times (based on index) Can be nested Each loop is closed with end. N=10; N=10; for for I = 1:2:N 1:2:N for for J = 1:N 1:N A(I,J) = 1/(I+J-1); end end end end

14 The while loop Similar to other programming languages Repeats loop until logical condition returns FALSE. Can be nested. Stopping infinity loop: Ctrl+C Ctrl+break I=1; I=1; N=10; N=10; while while I<=N I<=N J=1; J=1; while while J<=N J<=N A(I,J)=1/(I+J-1); J=J+1; end end I=I+1; end end

15 Problem Write a script that asks for a temperature (in degrees Fahrenheit) computes the equivalent temperature in degrees Celcius. The script should keep running until no number is provided to convert. use isempty C=5*(F-32)/9

16 Solution while while 1 % use use of of an an infinite loop loop TinF TinF = input('temperature in in F: F: '); '); % get get input input if if isempty(tinf) % how how to to get get out out break break end end TinC TinC = 5*(TinF - 32)/9; % conversion disp(' ') ') disp([' ==> ==> Temperature in in C = ',num2str(tinc)]) disp(' ') ') end end

17 Repetition: Animation demo The function movie replays a sequence of captured frames Construct a movie of a 360 tour around the Matlab logo % logomovie make make movie movie of of degree degree logo logo tour tour logo; logo; no_frames=40; dtheta=360/no_frames; for forframe frame = 1:no_frames, camorbit(dtheta,0) M(frame) = getframe(gcf); end end % now now display display captured movie movie movie(gcf,m); logomovie.m

18 Functions Functions describe subprograms Take inputs, generate outputs Have local variables (invisible in global workspace) Core MATLAB (Built-in) Functions sin, abs, exp,... Can t be displayed on screen MATLAB-supplied M-file Functions mean, linspace, Can be displayed on screen User-created M-file Functions

19 Core MATLAB (Built-in) Functions Elementary built-in functions >> help elfun % a list of these functions sin sin % Sine. exp exp % Exponential. abs abs % Absolute value. round % Round towards nearest integer. Special Math functions >> help specfun lcm lcm cart2sph % Least common multiple. % Transform Cartesian to to spherical % coordinates. Special functions - toolboxes Each toolbox has a list of special functions that you can use

20 Structure of a Function M-fileM Keyword: function Function Name (same as file name.m) Output Argument(s) Input Argument(s) Online Help MATLAB Code function y = mean(x) % MEAN MEAN Average or or mean mean value. % For For vectors, MEAN(x) returns the the mean mean value. % For For matrices, MEAN(x) is is a row row vector % containing the the mean mean value value of of each each column. [m,n] [m,n] = size(x); if if m == == 1 m = n; n; end end y = sum(x)/m;»output_value = mean(input_value) Command Line Syntax

21 Multiple Input & Output Arguments function function r = ourrank(x,tol) Multiple Input % OURRANK OURRANK Rank Rank of of a matrix matrix Arguments (, ) s = svd(x); if if (nargin == == 1) 1) Multiple Output tol tol = max(size(x))*s(1)*eps; Arguments [, ] end end r = sum(s sum(s > tol); tol); function function [mean,stdev] = ourstat(x) % OURSTAT OURSTAT Mean Mean & std. std. deviation deviation [m,n] [m,n] = size(x); if if m == == 1 m = n; n; end end mean mean = sum(x)/m; stdev stdev = sqrt(sum(x.^2)/m mean.^2);» RANK = ourrank(rand(5),0.1);» [MEAN,STDEV] = ourstat(1:99);

22 nargin, nargout, nargchk nargin number of input arguments - Many of Matlab functions can be run with different number of input variables. nargout number of output arguments - efficiency nargchk check if number of input arguments is between some low and high values

23 Workspaces in MATLAB MATLAB (or Base) Workspace: For command line and script file variables. Function Workspaces: Each function has its own workspace for local variables. Name of Input/output variables can be either equal or different then the variable name in the calling workspace. Communicate to Function Workspace via inputs & outputs. Global Workspace: Global variables can be shared by multiple workspaces. (Must be initialized in all relevant workspaces.) Initialize global variables in all relevant workspaces:»global variable_name Initialize global variables in the source workspace before referring to them from other workspaces.

24 Tips for using Global Variables DON T USE THEM If you absolutely must use them: Avoid name conflicts >>whos global %shows the contents of the global workspace >>clear global %erases the variable from both local and global workspaces. >>isglobal()

25 MATLAB Calling Priority High variable built-in function subfunction private function MEX-file P-file M-file» cos='this cos='this string.'; string.';» cos(8) cos(8) ans ans = r» clear clear cos cos» cos(8) cos(8) ans ans = Low

26 Add path >> addpath C:\EMEM899\Somedirectory Set path

27 Visual Debugging Select Workspace Set Auto- Breakpoints Set Breakpoint Clear Breaks Step In Single Step Continue Quit Debugging

28 Example: Visual Debugging (2) Editor/Debugger opens the relevant file and identifies the line where the error occurred. Current Location Current Workspace (Function)

29 Example: Visual Debugging (3) Error message Debug Mode Access to Function s Workspace

30 Some Useful MATLAB commands what List all m-files in current directory dir List all files in current directory ls Same as dir type test Display test.m in command window delete test Delete test.m cd a: Change directory to a: chdir a: Same as cd pwd Show current directory which test Display current directory path to test.m why In case you ever needed a reason

31 Problem Write a function that asks for a temperature (in degrees Fahrenheit) computes the equivalent temperature in degrees Celcius. The function should give an error massage in case no number is provided to convert. use nargin.

32 Solution function TinC=temp2(TinF) if if nargin==0 % if if there is is no no input disp('no temparture was was entered'); TinC=nan; else TinC = 5*(TinF - 32)/9; % conversion disp(' ') ') disp([' ==> ==> Temperature in in C =',num2str(tinc)]) disp(' ') ') end end

33 To read files in MATLAB Input if the file is an ascii table, use load if the file is ascii but not a table, file I/O needs fopen and fclose Reading in data from file using fopen depends on type of data (binary or text) Default data type is binary

34 What Is GUIDE? Graphical User Interface Design Environment provides a set of tools for creating graphical user interfaces (GUIs). GUIDE automatically generates an M-file that controls how the GUI operates. Starting GUIDE: >> guide OR: axes Push buttons Static text Pop-up menu

35 GUIDE Tools - The Layout Editor In the Quick Start dialog, select the Blank GUI (Default) template Component panel Layout area Display names of components: File preferences Show names in component palette Lay out your GUI by dragging components (panels, push buttons, pop-up menus, or axes) from the component palette, into the layout area Drag to resize

36 Using the Property Inspector Labeling the Buttons Select Property Inspector from the View menu. Select button by clicking it. Fill the name in the String field. Property Inspector Activate GUI

37 Programming a GUI Callbacks are functions that execute in response to some action by the user. A typical action is clicking a push button. You program the GUI by coding one or more callbacks for each of its components. A GUI's callbacks are found in an M-file that GUIDE generates automatically. Callback template for a push button:

38 handles structure Save the objects handles: handles.objectname Save global data can be used outside the function. Example: popup menu: Value user choice of the popup menu