MATLAB Second Seminar

1. MATLABSecond 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. 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

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

5. 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, … Ca be displayed on screen • User-created M-file Functions

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

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

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

9. 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

10. 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.

11. 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()

12. MATLAB Calling Priority High variable built-in function subfunction private function MEX-file P-file M-file Low » cos='This string.'; » cos(8) ans = r » clear cos » cos(8) ans = -0.1455

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

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

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

16. 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

17. 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.

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

19. MATLAB Input To read files in • 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”

20. 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: Push buttons axes Static text Pop-up menu

21. GUIDE Tools - The Layout Editor • In the Quick Start dialog, select the Blank GUI (Default) template • 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 Component panel Drag to resize Layout area

22. 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. Activate GUI Property Inspector

23. 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:

24. 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