Function definition syntax in MATLAB

Introduction

Functions help you organize your code into small, reusable pieces that do one job well.

When you want to repeat a task many times without rewriting code.

When you want to make your code easier to read and understand.

When you want to break a big problem into smaller, manageable parts.

When you want to test parts of your code separately.

When you want to share code with others or use it in different programs.

Syntax

MATLAB

function [output1, output2, ...] = functionName(input1, input2, ...)
    % Your code here
end

The keyword function starts the function definition.

You list outputs in square brackets and inputs in parentheses.

Examples

A simple function that takes one input and returns its square.

MATLAB

function y = squareNumber(x)
    y = x^2;
end

A function with two outputs: sum and difference of two inputs.

MATLAB

function [sum, diff] = addSubtract(a, b)
    sum = a + b;
    diff = a - b;
end

A function with no inputs and no outputs that just prints a message.

MATLAB

function greet()
    disp('Hello!')
end

Sample Program

This defines a function that multiplies a number by 3. Save as multiplyByThree.m. Then in the command window: answer = multiplyByThree(5); disp(['5 multiplied by 3 is ', num2str(answer)]);

MATLAB

function result = multiplyByThree(num)
    result = num * 3;
end

Important Notes

Function files must be saved with the same name as the function (e.g., multiplyByThree.m).

Use comments inside functions to explain what the code does.

Functions can have multiple inputs and outputs, but keep them simple for clarity.

Summary

Functions start with the keyword function followed by outputs, name, and inputs.

They help make code reusable and easier to understand.

Always save function code in a file named after the function.

Practice

1. Which of the following correctly describes the purpose of a function in MATLAB?

easy

A. To run MATLAB without installing it

B. To store data permanently on the computer

C. To create reusable blocks of code that perform specific tasks

D. To display graphics on the screen

Solution

1. Step 1: Understand what functions do

   Functions are designed to perform specific tasks repeatedly without rewriting code.

2. Step 2: Match purpose with options

   Only To create reusable blocks of code that perform specific tasks describes reusable code blocks, which is the main purpose of functions.

3. Final Answer:

   To create reusable blocks of code that perform specific tasks -> Option C

4. Quick Check:

   Function purpose = reusable code [OK]

Hint: Functions are for reusable code blocks [OK]

Common Mistakes:

• Confusing functions with data storage
• Thinking functions display graphics by default
• Assuming functions run MATLAB itself

2. Which of the following is the correct syntax to define a function named addNumbers that takes two inputs a and b and returns their sum c?

easy

A. function addNumbers = c(a, b)

B. function c = addNumbers(a, b)

C. def addNumbers(a, b):

D. func c(a, b) = addNumbers

Solution

1. Step 1: Recall MATLAB function syntax

   MATLAB functions start with the keyword 'function', then output(s), '=', function name, and input(s) in parentheses.

2. Step 2: Check each option

   function c = addNumbers(a, b) matches this syntax exactly. Options A, B, and D use incorrect keywords or order.

3. Final Answer:

   function c = addNumbers(a, b) -> Option B

4. Quick Check:

   function keyword + output = name(inputs) [OK]

Hint: Start with 'function', then output = name(inputs) [OK]

Common Mistakes:

• Using Python syntax like 'def'
• Placing function name before output incorrectly
• Using wrong keywords like 'func'

3. What will be the output of the following MATLAB function call?

function y = squareNum(x)
    y = x^2;
end

result = squareNum(4); disp(result);

medium

A. Error: Undefined function

B. 8

C. 4

D. 16

Solution

1. Step 1: Understand the function behavior

   The function squares the input number x by calculating x^2.

2. Step 2: Calculate the output for input 4

   4 squared is 4 * 4 = 16.

3. Final Answer:

   16 -> Option D

4. Quick Check:

   4 squared = 16 [OK]

Hint: Square input number to get output [OK]

Common Mistakes:

• Confusing ^ with multiplication
• Expecting addition instead of power
• Assuming function is undefined

4. Identify the error in the following MATLAB function definition:

function result = multiply(a, b)
result = a * b
end

medium

A. Missing semicolon after the multiplication statement

B. Function name does not match the file name

C. Incorrect use of the multiplication operator

D. Missing 'function' keyword

Solution

1. Step 1: Check syntax inside the function

   MATLAB statements should end with a semicolon to suppress output; here, it's missing after 'result = a * b'.

2. Step 2: Verify other parts

   The function keyword is present, the operator is correct, and file name matching is not shown but assumed correct.

3. Final Answer:

   Missing semicolon after the multiplication statement -> Option A

4. Quick Check:

   Statements need semicolon [OK]

Hint: End statements with semicolon to avoid errors [OK]

Common Mistakes:

• Forgetting semicolons after statements
• Assuming multiplication operator is wrong
• Ignoring file name and function name match

5. You want to create a MATLAB function named convertToFahrenheit that takes a Celsius temperature input and returns the Fahrenheit equivalent. Which of the following is the correct complete function definition?

hard

A. function F = convertToFahrenheit(C)
F = (C * 9/5) + 32;
end

B. function convertToFahrenheit = F(C)
F = (C + 32) * 9/5;
end

C. function F = convertToFahrenheit(C)
F = (C - 32) * 5/9;
end

D. function F = convertToFahrenheit(C)
F = C * 5/9 + 32;
end

Solution

1. Step 1: Recall the formula for Celsius to Fahrenheit

   The correct formula is Fahrenheit = (Celsius * 9/5) + 32.

2. Step 2: Check each function definition

   function F = convertToFahrenheit(C) F = (C * 9/5) + 32; end uses the correct formula and syntax. Options A, C, and D have wrong formulas or incorrect output variable assignment.

3. Final Answer:

   function F = convertToFahrenheit(C) F = (C * 9/5) + 32; end -> Option A

4. Quick Check:

   Celsius to Fahrenheit formula = (C * 9/5) + 32 [OK]

Hint: Use correct formula: F = (C * 9/5) + 32 [OK]

Common Mistakes:

• Mixing Celsius to Fahrenheit with Fahrenheit to Celsius formula
• Swapping output and function name
• Missing semicolons or wrong operators