engr 111a - spring 20041 matlab – palm chapter 4, part 4 review and debugging class 12.1: palm...

ENGR 111A - Spring 2004 1

MatLab – Palm Chapter 4, Part 4Review and Debugging

Class 12.1:Palm Chapters 2.6-7 & 4.1-7


EXAM #2: NOV. 17, 2004

Details:Wednesday, Nov. 17, 20046:30-8:00 p.m.Same room as last time

Bring: Drawing Tools, Calculator, Pencil

Coverage: Material from Lecture 6.1 through 11.2.


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


LEARNING OBJECTIVES

Students should be able to: Run the Matlab Editor/Debugger

Window Set Preferences Follow Matlab Error Messages Debug User-Defined Programs


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


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


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.


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).


EXAMPLE ERROR MESSAGE

An M-file contains:x = 7;y = 8;if x = y x = y$2else x = y(3end

Running at the command prompt gives:>> temp??? Error: File: C:\Programs\MATLAB6p5\work\temp.m

Line: 3 Column: 6Assignment statements do not produce results. (Use = =

to test for equality.)


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!


EXAM #2 REVIEW

Chapters 2.6-7 and 4.2-6 in the Palm Matlab Book


REVIEW TOPICS

2.6 Cell Arrays 2.7 Structure 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)


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.

Easterwood Nov. 6, 2004

[10 14 16 20] [2 4 5 7]


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))


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 2nd grade of all three students and display the result in the command window


SOLUTION% Create structurestudent(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 gradesave_grade = sum([student.grade])/… length(student);% Display 2nd gradedisp(ave_grade(2))


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)


EXAMPLE

Write a function to compute the volume and surface area of a sphere given the diameter as input.

Volume:V = 4r3/3

Surface AreaA = 4r2


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;


SOLUTION CONTINUED>> sphere(4)ans = 268.0826

>> V = sphere(4)V = 268.0826

>> [V, A] = sphere(4)V = 268.0826A = 201.0619


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


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 < y) & (y > z) | “or” links logical expressions

e.g. (x < y) | (y > z)


ORDER OF PRECEDENCE

Comparison statements are evaluated according to the following strict order of precedence:1. Parenthesis starting with innermost2. Arithmetic operators and ~ evaluated

from left to right3. Relational operators evaluated from

left to right4. & operator (logical AND)5. | operator (logical OR)


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?


SOLUTION>> x = [6, 3, 9]>> y = [14, 0, 9]>> z = ~xz = 0 0 0>> z = ~x > yz = 0 0 0>> z = ~(x > y)z = 1 0 1>> z = x > ~yz = 1 1 1>> x ~> y??? x ~> y |Error: Missing operator, comma, or semicolon.

Notice, Matlab is pointingto where it found an error


4.4 SELECTION STRUCTURES

if…elseif…else…end. Most general form:

if logical expression 1statement group 1

elseif logical expression 2statement group 2

elsestatement group 3

end

Only one statement group will execute no matter what!


4.5 ITERATION STRUCTURES

for…end and while…end loops

for variable = start:step:stop statementsend

while logical expression statements (must change logical expression)end


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).


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


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 endend


SOLUTION: WHILE-LOOPr = 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


4.6 SWITCH CASE switch…end. Most general form:

switch variable case value1 statement group 1 case value2 statement group 2 otherwise default caseend

Name of avariable containingthe value of the switch parameter

Possible values that the switch parameter mighthave


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.


SOLUTIONn = 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);endgpr = total / sum(hours);


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.


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

engr 111a - spring 20041 matlab – palm chapter 4, part 4 review and debugging class 12.1: palm...

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