EE2372 Programming elements in MATLAB

1. EE2372 Programming elements in MATLAB Dr. Jose Gerardo Rosiles Spring 2010 TTh 10:30-11:50 am

2. Variables • Store numerical and alphanumerical values • x = 10, z=9.5, s=‘cat’ • Can use more meaningful names mixing letters, numbers and underscore character • Variables must start with a letter • Temperature = 45, name = ‘Peter’, number_of_students = 31

3. Relational operators • >, >=, <=, < • == compares if two values are equal • != compares if two values are not equal • Result is a BOOLEAN decision: TRUE of FALSE • How do we represent boolean decisions numerically? • TRUE = 1 • FALSE = 0

4. Decision commands • Logical operators allow us to compare values • What are comparisons useful for? • Make decision within your program • In most computer languages decision are made using the if-then-else statement • General syntax if ( relational operation is TRUE) do action A else do action B end

5. Decision command • Example: A smoke detector • What are the steps taken by the program running by the microprocessor inside a smoke detector? • Let’s implement in MATLAB, syntax varies a little if ( relational operation) do A else do B end

6. Logical operators • AND, OR, NOT • Also useful to make decisions • Make more complex logic statements • In MATLAB: & = AND | = OR ~ = NOT

7. Example of compound statements if ( (x > 5) & (x < 10) ) If ( ( (x+y) <= z ) | (y>10) ) • What is the hierarchy of these commands?

8. More on variables • The = operator has a different meaning than in mathematics. • What is the meaning of: x = x + 1 ? In Math: 0=1???? In programming: How does the microprocessor do it? • Equal “=“ is an assignment operator • What about x = x + y, where y is another variable?

9. Looping structures • An important type of variable are arrays. • Array a group of variables with the same name, indexed by a unique integer • Recall sequences and series from calculus • Example in MATLAB: grade = zeros(1,10); Creates 10 variables names grade INDEXED by an integer from 1 to 10 : grade(1) = 80; grade(5) = 10; etc.

10. Looping Structures • Allow you to repeat the same process many times. • We have for loops and while loops • for loops consist of an initial value, an increment and a final value • while loops require a stopping condition.

11. for loops • MATLAB structure forinitial value: increment: final value //Do something end Example: Compute the average value of the grade() array.

12. for loops Memory map grade = zeros(1,10); avg = 0; sum = 0; for?: ?: ? //How do we accumulate the values of grade? end avg = sum/10; Steps taken by microprocessor on first iteration Fetch sum Fetch grade(1) Add sum and grade(1) Store result in sum

13. while loops grade = zeros(1,10); avg = 0; sum = 0; i = 1; while ( stop condition ) sum = sum + grade(i); i = i + 1; end avg = sum/10; i < 10

14. Input and output in MATLAB • To get user input we have the special function “input” that allows to display a message Temperature = input(‘Enter toda’stempetature: ‘); • Write value at prompt and press enter to continue with program

15. Input and output in MATLAB • For output there are more variations: disp(‘my message’); error(‘to print messages when an error condition has … occurred’) • File print file function, very advanced formatting: fprintf(1, ‘my string %d %f %s’, int_val, float_val, … str_val);

16. A Complete Example %% program to convert number grades to letter graders grade = [80 70 75 90 65 95 75 80]; fprintf(1, ' Student Grade Letter Grade \n'); fori = 1:1:8 if(grade(i)>=90) letter_grade = 'A'; elseif (grade(i) >= 80) letter_grade = 'B'; elseif (grade(i) >= 70) letter_grade = 'C'; elseif (grade(i) >= 60) letter_grade = 'D'; else letter_grade = 'F'; end fprintf(1,' %d %d %c \n', i, grade(i), letter_grade); end Formatted Program Output Student Grade Letter Grade 1 80 B 2 70 C 3 75 C 4 90 A 5 65 D 6 95 A 7 75 C 8 80 B

17. Modularity • Consider the previous program %% program to convert number grades to letter graders grade = [80 70 75 90 65 95 75 80]; fprintf(1, ' Student Grade Letter Grade \n'); fori = 1:1:8 if(grade(i)>=90) letter_grade = 'A'; elseif (grade(i) >= 80) letter_grade = 'B'; elseif (grade(i) >= 70) letter_grade = 'C'; elseif (grade(i) >= 60) letter_grade = 'D'; else letter_grade = 'F'; end fprintf(1,' %d %d %c \n', i, grade(i), letter_grade); end Some parts of the program may look too cluttered, making the program confusing

18. Modularity • We can improve the program in terms of functionality and clarity using functions. • Functions (aka subroutines) encapsulate certain program behaviors or patterns that repeat over and over in your program. • This encapsulation • visually makes your program read better (less clutter) and • allows the “extension” of the language to add customized functionality

19. Modularity • Let’s analyze our program • The chain of if-else statements is hard to read. • Let encapsulate this functionality into a function. functionoutput_value = function_name(param1, pararm2, param3, ….) // body of function end

20. Modularity and Functions %% program to convert number grades to letter graders grade = [80 70 75 90 65 95 75 80]; fprintf(1, ' Student Grade Letter Grade \n'); fori = 1:1:8 if(grade(i)>=90) letter_grade = 'A'; elseif (grade(i) >= 80) letter_grade = 'B'; elseif (grade(i) >= 70) letter_grade = 'C'; elseif (grade(i) >= 60) letter_grade = 'D'; else letter_grade = 'F'; end fprintf(1,' %d %d %c \n', i, grade(i), letter_grade); end function letter = convert_to_letter(in_grade) if (in_grade>=90) letter_grade = 'A'; elseif (in_grade >= 80) letter_grade = 'B'; elseif (in_grade >= 70) letter_grade = 'C'; elseif (in_grade >= 60) letter_grade = 'D'; else letter_grade = 'F'; end letter = letter_grade; end letter_grade = convert_to_letter( grade(i) );

21. Exercise • Write a function to compute . • Let be a non-negative integer ( ).