MATLAB Selection Statements, Loops, & Functions

Computation
How real numbers are digitally represented (“floating point”)
Variable types
Selection statements (if and switch)
Loops (for and while)
User defined functions

Computation

Arithmetic Logic Unit (ALU) in a computer’s CPU executes fundamental arithmetic and logical operations. These are combined at higher levels of hardware and software to perform more sophisticated computations.

Knowing this can improve engineers’ understanding and performance in several areas:

Error awareness: Understanding potential sources of computational errors. For instance, floating-point arithmetic can lead to precision issues and rounding errors, which can accumulate in large-scale computations.
Algorithm design: Understanding the limitations of computer arithmetic helps design accurate numerical algorithms.
Debugging and troubleshooting: When unexpected results occur in computations, understanding the underlying arithmetic can be crucial in identifying and resolving issues.

MATLAB Recap

            % assign a value to variable t

            t = 5;

            % calculate the value of another variable x

            x = 3*sin(5*pi*t/2);

            % if x satisfies some condition, output message to console

            if x < 9

                display('Hello World');

            end

MATLAB Statements/Commands

MATLAB statements are instructions; they are not equations.

Example:

                a = 5    % Assign the value on the right side to the variable on the left

                a == 5   % Check if the right and left sides are equal; returns true if equal, false otherwise

In MATLAB:

= is an assignment operator.
== is a comparison operator used in logical expressions.

Some Variable Types in MATLAB

Variable Type	Memory Size	Examples
Double	8 Bytes	5, 1.2345, pi, -7.3e5, …
Character	2 Bytes	'x', 'y', '0', …
Logical	1 Byte	false, true

Propositional Logic

Truth Tables for Conjunction (“and”), Disjunction (“or”)

P	Q	P & Q	P \| Q
T	T	T	T
T	F	F	T
F	T	F	T
F	F	F	F

Example of Composite Statement

P	Q	R	Q \| R	P & (Q \| R)
T	T	T	T	T
T	T	F	T	T
T	F	T	T	T
T	F	F	F	F
F	T	T	T	F
F	T	F	T	F
F	F	T	T	F
F	F	F	F	F

MATLAB Examples

P = (1 < (2/pi))
Q = (49 == 7^2)
P & Q
P | Q

For more details and examples on propositional logic, please visit: Propositional Logic

Selection Statements

Basic if-else Statement

if-elseif-else Statement

                if y == 20

                    x = 5

                elseif y == 35

                    x = 20

                else

                    x = -4

                end

switch Statement

Loops

For-loop

                for n = 1:7

                    % computations

                    % 

                end

Note: The for-loop executes a block of code a specified number of times. In this example, the loop runs 5 times with n taking values from 1 to 7.

While-loop

                n = 1

                while n ≤ 7

                    % computations

                    % 

                    n = n + 1

                end

Note: The while-loop executes a block of code as long as a specified condition is true. Remember to update the loop variable (n) inside the loop to avoid infinite loops.

Functions

User-defined function examples:

Techique 1: All in one file

script_1.m

                x = 15;

                y = 19;

                z = myfunc(x,y);

                function r = myfunc(a,b)

                    l = m^2 - n;

                end

Note: In MATLAB, when using local functions in a script file (Techique 1), the functions must be placed at the end of the file. The main script code comes first, followed by all function definitions.

Method 2: Separate function file

mainscript.m

                x = 15;

                y = 19;

                z = myfunc(x,y);

myfunc.m

                function l = myfunc(m,n)

                    % MYFUNC Example custom function

                    % Computes m squared minus n

                    l = m^2 - n;

                end

Note: When using separate files (Techique 2), the function file must have the same name as the function (myfunc.m) and be located in the MATLAB path. This is the traditional approach for organizing larger projects.

Practice Questions: Test your Knowledge

View the Questions

Answers to the Practice Questions

View the Answer

MATLAB Selection Statements, Loops, & Functions

Computation

MATLAB Recap

MATLAB Statements/Commands

Example:

Some Variable Types in MATLAB

Propositional Logic

Truth Tables for Conjunction (“and”), Disjunction (“or”)

Example of Composite Statement

MATLAB Examples

Selection Statements

Basic if-else Statement

if-elseif-else Statement

switch Statement

Loops

For-loop

While-loop

Functions

Practice Questions: Test your Knowledge

Answers to the Practice Questions

Additional Exercises

Practice Exercise 1

Solution to Exercise 1

Practice Exercise 2

Solution to Exercise 2

Practice Exercise 3

Solution to Exercise 3

Practice Exercise 4

Solution to Exercise 4

Practice Exercise 5

Solution to Exercise 5

Practice Exercise 6

Solution to Exercise 6

Practice Exercise 7

Solution to Exercise 7

Practice Exercise 8

Solution to Exercise 8

Practice Exercise 9

Solution to Exercise 9

Practice Exercise 10

Solution to Exercise 10

Practice Exercise 11

Solution to Exercise 11

Practice Exercise 12

Solution to Exercise 12

Practice Exercise 13

Solution to Exercise 13

Practice Exercise 14

Solution to Exercise 14

Practice Exercise 15

Solution to Exercise 15

Practice Exercise 16

Solution to Exercise 16

Practice Exercise 17

Solution to Exercise 17

Practice Exercise 18

Solution to Exercise 18

Practice Exercise 19

Solution to Exercise 19

Practice Exercise 20

Solution to Exercise 20

Practice Exercise 21

Solution to Exercise 21