Function handles in MATLAB

Introduction

Function handles let you store and use functions like variables. This helps you call functions later or pass them around easily.

When you want to pass a function as input to another function.

When you want to call a function multiple times without rewriting its name.

When you want to create flexible code that can use different functions.

When you want to store a function in a variable for later use.

When you want to use anonymous functions for quick calculations.

Syntax

MATLAB

f = @functionName;

% or for anonymous functions:
f = @(input) expression;

Use the @ symbol before the function name to create a function handle.

Anonymous functions let you write small functions without creating a separate file.

Examples

Create a handle to the built-in sine function and call it with pi/2.

MATLAB

f = @sin;
result = f(pi/2);

Create an anonymous function to square a number and use it.

MATLAB

square = @(x) x.^2;
result = square(4);

Create a handle to the max function and find the maximum in an array.

MATLAB

f = @max;
result = f([1, 5, 3]);

Sample Program

This program creates a function handle 'square' to calculate squares. Then it uses arrayfun to apply it to each number in the array and displays the results.

MATLAB

square = @(x) x.^2;
nums = [1, 2, 3, 4];
squares = arrayfun(square, nums);
disp(squares);

Important Notes

Function handles can be passed as arguments to other functions like arrayfun or ode45.

Anonymous functions are useful for quick, simple operations without making a separate file.

Remember to use dot operators (like .^) inside anonymous functions to work element-wise on arrays.

Summary

Function handles let you treat functions like variables.

Use @ to create a handle to named or anonymous functions.

They help make your code flexible and reusable.

Practice

1. What does a function handle in MATLAB allow you to do?

easy

A. Store a reference to a function that can be called later

B. Create a new variable type

C. Automatically run a function without calling it

D. Convert a function into a string

Solution

1. Step 1: Understand what a function handle is

   A function handle is a way to refer to a function without executing it immediately.

2. Step 2: Identify the purpose of function handles

   They let you store and pass functions as variables to call later.

3. Final Answer:

   Store a reference to a function that can be called later -> Option A

4. Quick Check:

   Function handle = reference to function [OK]

Hint: Think of function handles as pointers to functions [OK]

Common Mistakes:

• Confusing function handles with function execution
• Thinking function handles create new data types
• Assuming function handles convert functions to strings

2. Which of the following is the correct way to create a function handle for the built-in function sin in MATLAB?

easy

A. handle = sin();

B. handle = &sin;

C. handle = @sin;

D. handle = sin;

Solution

1. Step 1: Recall the syntax for creating function handles

   In MATLAB, function handles are created using the @ symbol followed by the function name without parentheses.

2. Step 2: Check each option

   handle = @sin; uses @sin which is correct. handle = sin(); calls sin immediately, C uses & which is not MATLAB syntax, and D assigns the function name as a variable without @ which is invalid.

3. Final Answer:

   handle = @sin; -> Option C

4. Quick Check:

   Use @ before function name to create handle [OK]

Hint: Use @ before function name, no parentheses [OK]

Common Mistakes:

• Adding parentheses when creating handles
• Using & instead of @
• Assigning function name without @

3. What is the output of the following MATLAB code?

f = @(x) x^2 + 3;
result = f(2);

medium

A. 5

B. Error

C. 10

D. 7

Solution

1. Step 1: Understand the anonymous function definition

   The function f takes input x and returns x squared plus 3.

2. Step 2: Calculate the function output for x = 2

   f(2) = 2^2 + 3 = 4 + 3 = 7.

3. Final Answer:

   7 -> Option D

4. Quick Check:

   2 squared plus 3 equals 7 [OK]

Hint: Plug input into function formula carefully [OK]

Common Mistakes:

• Forgetting to square the input
• Adding instead of multiplying
• Expecting syntax error from anonymous function

4. Identify the error in the following MATLAB code that tries to create a function handle:

g = @(x) x + 1;
h = @g(2);

medium

A. Cannot use parentheses when creating a function handle

B. Function handle syntax is correct

C. Missing semicolon after function handle

D. Function handle must be created with a string

Solution

1. Step 1: Analyze the function handle creation

   The first line correctly creates an anonymous function g. The second line tries to create a handle h using @g(2), which is incorrect syntax.

2. Step 2: Understand correct function handle usage

   The @ operator must be followed by a function name or anonymous function without parentheses. Using parentheses calls the function, which is not allowed when creating a handle.

3. Final Answer:

   Cannot use parentheses when creating a function handle -> Option A

4. Quick Check:

   No parentheses allowed after @ when creating handles [OK]

Hint: No parentheses after @ when defining handles [OK]

Common Mistakes:

• Using parentheses after @
• Confusing function call with handle creation
• Thinking semicolon is required for correctness

5. You want to create a function handle that takes two inputs and returns their product plus 5. Which of the following anonymous function definitions is correct?

hard

A. f = @(x y) x * y + 5;

B. f = @(x, y) x * y + 5;

C. f = @(x, y) (x + y) * 5;

D. f = @(x, y) x * y + 5()

Solution

1. Step 1: Check the syntax for anonymous functions with multiple inputs

   Inputs must be separated by commas inside parentheses after @.

2. Step 2: Verify the expression matches the requirement

   f = @(x, y) x * y + 5; multiplies x and y, then adds 5, which matches the problem. f = @(x y) x * y + 5; misses the comma, C changes the operation, and D has invalid syntax with 5().

3. Final Answer:

   f = @(x, y) x * y + 5; -> Option B

4. Quick Check:

   Use commas between inputs and correct expression [OK]

Hint: Separate inputs with commas and write correct formula [OK]

Common Mistakes:

• Omitting commas between inputs
• Changing the math operation accidentally
• Adding parentheses after constants