MATLAB

1. MATLAB Lecture Two (Part I) Thursday, 3 July 2003

2. Chapter 4 Programming in MATLAB

3. M-Files • Script file: a collection of MATLAB commands • Function file: a definition file for one function

4. Script Files • Any valid sequence of MATLAB commands can be in the script files. • Variables defined/used in script files are global, i.e., they present in the workspace.

5. Script File Example • Linear equation with a parameter r - solve the equation 5 x + 2r y + r z = 2, 3 x + 6 y + (2r-1) z = 3, 2 x + (r-1) y + 3r z = 5.

6. Script File Example % ---This is the script file `solvex.m' % It solves equation (4.1) for x and also % calculate det(A). A = [5 2*r r; 3 6 2*r-1; 2 r-1 3*r]; b = [2; 3; 5]; det_A = det(A) x = A\b

7. Script Files: Caution • Never name a script file the same as the name of a variable it computes. • The name of a script file must begin with a letter, followed by letters, digits, or underscores, with up to 19 character long, with extension .m.

8. Script Files: Caution • All variables generated by a script file are left in the workspace. Avoid name clashes with built-in functions. • Use the command exist('name') to check if the name exists.

9. Function Files • A function file is also an M-file, except that the variables in a function file are all local. • Function file is like a subroutine in FORTRAN, procedure in Pascal, or function in C.

10. Syntax of Function Definition Function [output variables] = functionname(input variables); E.g., function [rho,H,F] = motion(x,y,z); function [theta] = angleTH(x,y); function theta = THETA(x,y,z); function [ ] = circle( r ); function circle( r );

11. Some comments on function definition • Unlike other programming languages, data types are not specified in argument list and return values. • MATLAB functions can return a list of values (a vector).

12. Function M-file • The name of the function M-file must be the same as the name of the function (case sensitive). • E.g., function theta = THETA(x,y) file name should be THETA.m

13. Anatomy of a Function File function [xout, yout] = funcname(xin, yin); % FUNCNAME : compute … % write on-line help comment % include your name and date x = blah; y = moreblah; xout = …, yout = ...

14. Executing of a Function • If the function is defined by function [rho,H,F] = motion(x,y,t); • The function can be called (used) as [r, ang, force] = motion(xt,yt,time); • Or motion(2, 3.5, 0.001);

15. Function as Argument • The name of the function is passed as a string, quoted with single quotes. • E.g., integration('sin', 0, 1.0)

16. Function as Argument • feval evaluates a function whose name is specified as a string (e.g. passed by argument list) • E.g., feval('sin', 0.3) • is the same as sin(0.3)

17. Integration Example • Function definition function res = integration(f,a,b) … feval(f, x); … • Use integration('sin', 0, 1)

18. Language-Specific Features • Use of comments to create on-line help, H1 line • Line continuation, use … at the end of a line

19. Global Variable in Function Function xdot = ode1(t,x); % ODE1 : function to … global k_value c_value xdot = k_value + ...

20. Loops, branches, control-flow branches loop flow

21. For Loop for m=1:100 y(m) = sin(1.0/m); end for n=100:-2:0, k=…, end n runs over 100, 98, 96, …, 2, 0.

22. While Loop num = 0; v = 1; i = 1; while num < 10 num = num + 1; v = v * 2^num; … end

23. IF-Elseif-Else if i > 5 k = i; elseif (i>1) & (j==20) k = 5*i + j; else k = 1; end

24. Switch-Case-Otherwise switch flag case value1 block1 case value 2 block2 … otherwise blockdefault end

25. Switch-Case-Otherwise switch color case 'red' c = [1 0 0]; case 'green' c = [0 1 0]; case 'blue' c = [0 0 1]; otherwise error('invalid choice') end

26. Break • The command `break' inside a for or while loop terminates the execution of the loop. • Unlike C/C++, no need to put break in the switch statement.

27. Return function animatebar(t0, tf, x0); % ANIMATEBAR do such and ... disp('Do you want to see …') ans = input('Enter 1 if yes, 0 if No'); if ans==0 return else plot(x, …) end

28. Interactive Input • Input('string') print the 'string' and wait for user input • E.g. n = input('Enter a number n:'); more = input('More simulation? 'Y/N', 's'); The input will be a string

29. Keyboard • The commend `keyboard' return control to the keyboard from script or function. • Type `return' makes control back to the script or function. • Useful for debugging.

30. Menu • coord = menu('Menu Name', 'A', 'B', 'C'); creates a menu choice with name `Menu Name', and three buttons labeled `A', `B', and `C'. The return value coord is 1 for choice A, 2 for B, and 3 for C.

31. C style I/O • MATLAB supports many standard C-language file and I/O functions. fopen opens a file fclose closes a file fscanf reads formatted data fprintf writes formatted data fgets reads a line

32. Advanced Data Objects • Multidimensional array • e.g. A(4,4,2) • Structure • fallsem.couse = 'cs101'; • fallsem.prof = 'Turing'; • fallsem.score = [80 75 95]; • Cells • C = {0.1 's' fallsem};

33. Exercise 1 • Define a function that (1) ask the user to enter a sequence of numbers, (2) sort the numbers in ascending order, (3) return the sorted numbers.

34. How to Submit • Send your diary file and *m file by email to Nguyen Ngoc Son g0200756@nus.edu.sg