1. ENGR 111A - Spring 20041 MatLab – Palm Chapter 4, Part 4 Review and Debugging Class 12.1: Palm Chapters 2.6-7 & 4.1-7

2. ENGR 111A - Spring 20042 EXAM #2: NOV. 17, 2004 Details: Wednesday, Nov. 17, 2004 6:30-8:00 p.m. Same room as last time Bring: Drawing Tools, Calculator, Pencil Coverage: Material from Lecture 6.1 through 11.2.

3. ENGR 111A - Spring 20043 EXAM #2, CONTINUED Alternate Exam Times: If you have a verifiable conflict, you can arrange with the instructor to take the exam at: 5:00 pm CVLB 420 with Kohutek By appointment Arrangements MUST be made by Nov. 16, 2004

4. ENGR 111A - Spring 20044 LEARNING OBJECTIVES Students should be able to: Run the Matlab Editor/Debugger Window Set Preferences Follow Matlab Error Messages Debug User-Defined Programs

5. ENGR 111A - Spring 20045 4.7 DEBUGGING(P. 201) Activate the Editor/Debugger window and browse the menu items Set Preferences is in the File menu Text formatting tools (indents) are in the Text menu Find and replace tools are in the Edit menu

6. ENGR 111A - Spring 20046 DEBUGGING MENU Load one of your old script files into the debug window and make sure that it has “the focus” (is active). Click on the “run” item in the Debug menu. Notice the variables that were created in the workspace. You can find the values in the Command Window

7. ENGR 111A - Spring 20047 SOME HINTS Until you get some experience, do NOT expect your code to run correctly the first time; so, plan to do some debugging. Start at the top and look at the variable values and make sure you are getting what you expected. Point at the variable and a “hint” window with the values will appear.

8. ENGR 111A - Spring 20048 MORE HINTS If your code generates an error message, try a fix and re-run. This may take some research on your part. Starting at the bottom of your program, turn your statements into comments until you get something that actually runs. It is much harder to find algorithm errors (program runs but gives the wrong answer) than programming errors (program does not run or generates warnings).

9. ENGR 111A - Spring 20049 EXAMPLE ERROR MESSAGE An M-file contains: x = 7; y = 8; if x = y x = y$2 else x = y(3 end Running at the command prompt gives: >> temp ??? Error: File: C:\Programs\MATLAB6p5\work\temp.m Line: 3 Column: 6 Assignment statements do not produce results. (Use = = to test for equality.)

10. ENGR 111A - Spring 200410 EXAMPLE Matlab only reported the first error it found. It gives you a link to the position in the files where the error occurred. It tells you what type of error (assignment statements do not produce results). And it suggests a fix (use == to test for equality). However, it still takes a LOT of practice to understand these error messages!

11. ENGR 111A - Spring 200411 EXAM #2 REVIEW Chapters 2.6-7 and 4.2-6 in the Palm Matlab Book

12. ENGR 111A - Spring 200412 REVIEW TOPICS 2.6Cell Arrays 2.7Structure Arrays 3.2 Function Files 4.2 Relational Operators / Logical Variables 4.3 Logical Operators and Functions 4.4 if…end Conditional Structures 4.6 switch…end Selection Structures 4.5 Loops ( for…end and while…end )

13. ENGR 111A - Spring 200413 2.6 CELL ARRAYS Create a 2x2 Cell array named “climate” that stores the following table: Write a command to access the “5” in the matrix in the lower right-hand corner. EasterwoodNov. 6, 2004 [10 14 16 20][2 4 5 7]

14. ENGR 111A - Spring 200414 SOLUTION % Create Cell Array climate{1,1} = ‘Easterwood’; climate(1,2) = {‘Nov. 6, 2004’}; climate{2,1} = [10 14 16 20]; climate(2,2) = {[2 4; 5 7]}; % Access element 2,1 of lower % right-hand matrix disp(climate{2,2}(2,1))

15. ENGR 111A - Spring 200415 2.7 STRUCTURE ARRAYS Create a Structure Array called student with fields name and grade (grade will be an array with three exam grades in it) Fill in your structure with made up data for three students Write code to average the 2 nd grade of all three students and display the result in the command window

16. ENGR 111A - Spring 200416 SOLUTION % Create structure student(1).name = ‘Fritz Hertz’; student.grade = [87 92 78]; student(2).name = ‘Uli Bonn’; student(2).grade = [81 85 92]; student(3).name = ‘Max Plank’; student(3).grade = [94 95 92]; % Average grades ave_grade = sum([student.grade])/… length(student); % Display 2 nd grade disp(ave_grade(2))

17. ENGR 111A - Spring 200417 3.2 FUNCTION FILES User-defined function: take inputs and compute outputs; variables are local (that means they are deleted when the function finishes. General form: function [outputs] = my_name(inputs) At Matlab prompt type: >>[ouputs] = my_name(inputs)

18. ENGR 111A - Spring 200418 EXAMPLE Write a function to compute the volume and surface area of a sphere given the diameter as input. Volume: V = 4  r 3 /3 Surface Area A = 4  r 2

19. ENGR 111A - Spring 200419 SOLUTION function [V, A] = sphere(r) % r = radius of a sphere % V = Volume of the sphere % A = Area of the sphere V = 4*pi*r.^3/3; A = 4*pi*r.^2;

20. ENGR 111A - Spring 200420 SOLUTION CONTINUED >> sphere(4) ans = 268.0826 >> V = sphere(4) V = 268.0826 >> [V, A] = sphere(4) V = 268.0826 A = 201.0619

21. ENGR 111A - Spring 200421 4.2 RELATIONAL OPERATORS Matlab has 6 relational operators to make comparisons < less than > greater than <= less than or equal to >= greater than or equal to == equal to ~= not equal to Result of comparison: 1 is True and 0 is False

22. ENGR 111A - Spring 200422 4.3 LOGICAL OPERATORS Matlab has three logical operators ~ “not” is used to change true to false and false to true & “and” links logical expressions e.g. (x z) | “or” links logical expressions e.g. (x z)

23. ENGR 111A - Spring 200423 ORDER OF PRECEDENCE Comparison statements are evaluated according to the following strict order of precedence: 1.Parenthesis starting with innermost 2.Arithmetic operators and ~ evaluated from left to right 3.Relational operators evaluated from left to right 4.& operator (logical AND) 5.| operator (logical OR)

24. ENGR 111A - Spring 200424 EXAMPLES x = [6, 3, 9] y = [14, 0, 9] z = ~x returns z = ? z = ~x > y or z = (~x) > y returns z = ? z = ~(x > y) returns z = ? What would z = x>~y return? What would z = x~>y return?

25. ENGR 111A - Spring 200425 SOLUTION >> x = [6, 3, 9] >> y = [14, 0, 9] >> z = ~x z = 0 0 0 >> z = ~x > y z = 0 0 0 >> z = ~(x > y) z = 1 0 1 >> z = x > ~y z = 1 1 1 >> x ~> y ??? x ~> y | Error: Missing operator, comma, or semicolon. Notice, Matlab is pointing to where it found an error

26. ENGR 111A - Spring 200426 4.4 SELECTION STRUCTURES if…elseif…else…end. Most general form: if logical expression 1 statement group 1 elseif logical expression 2 statement group 2 else statement group 3 end Only one statement group will execute no matter what!

27. ENGR 111A - Spring 200427 4.5 ITERATION STRUCTURES for…end and while…end loops for variable = start:step:stop statements end while logical expression statements (must change logical expression) end

28. ENGR 111A - Spring 200428 BREAK AND CONTINUE break exits a loop. Used to halt a certain process, like a file read of unknown length. continue jumps to the end of a loop, but keeps on iterating. Used to “skip” bad values (like divide by zero).

29. ENGR 111A - Spring 200429 EXAMPLE Write a program to find the index of the maximum value in a matrix. First, write your program with a for…end loop Second, write your program with a while…end loop

30. ENGR 111A - Spring 200430 SOLUTION: FOR-LOOP [m,n] = size(A); max_val = A(1,1); for r = 1:m for c = 1:n if A(r,c) > max_val max_row = r; max_col = c; max_val = A(r,c); end

31. ENGR 111A - Spring 200431 SOLUTION: WHILE-LOOP r = 1; [m, n] = size(A); max_val = A(1,1); while r <= m c = 1; while c <= n if A(r,c) > max_val max_row = r; max_col = c; max_val = A(r,c); end c = c+1; end r = r+1; end

32. ENGR 111A - Spring 200432 4.6 SWITCH CASE switch…end. Most general form: switch variable case value1 statement group 1 case value2 statement group 2 otherwise default case end Name of a variable containing the value of the switch parameter Possible values that the switch parameter might have

33. ENGR 111A - Spring 200433 EXAMPLE Given the following grades and numbers of credit hours: grades = [‘A’, ‘B’, ‘B’, ‘C’] hours = [2, 3, 3, 4] Use a switch structure inside of a for loop to compute a student’s GPR Note that A=4.0, B=3.0, etc.

34. ENGR 111A - Spring 200434 SOLUTION n = length(grades); total = 0; for k = 1:n switch grades(k) case ' A ' value = 4.0; case ' B ' value = 3.0; case ' C ' value = 2.0; end total = total + value*hours(k); end gpr = total / sum(hours);

35. ENGR 111A - Spring 200435 ASSESSMENT Take out a sheet of paper and individually write a brief description of the MatLab topic that is the “muddiest” to you to date. Then, as a team, agree on a topic you would like for the TA to cover in help sessions. Write this on a sheet of paper along with your Team # and give this paper to the TA as you leave. Please note on you paper if you are usually missing a team member for class assignments or homework.

36. ENGR 111A - Spring 200436 ASSIGNMENT 12.1 Individual assignment Due: Tuesday, November 23, 2004 In-Class work that you did not finish by the end of this class. Study for the exam. Read Ch. 5.1-5.4 in the Palm Matlab book