Function handles in MATLAB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a function handle in MATLAB?

A function handle is a MATLAB data type that stores a reference to a function. It allows you to call the function indirectly and pass it as an argument to other functions.

beginner

How do you create a function handle for a built-in function like sin?

You create it using the @ symbol followed by the function name without parentheses, like this: f = @sin;

beginner

How can you use a function handle to call the function it refers to?

You use the function handle variable followed by parentheses with input arguments, for example: result = f(pi/2); calls the function and stores the output.

intermediate

What is an anonymous function in MATLAB and how is it related to function handles?

An anonymous function is a simple function you define in one line without a separate file. It is created using a function handle with the syntax: f = @(x) x^2;. The variable f is a function handle to this anonymous function.

intermediate

Why are function handles useful in MATLAB programming?

They let you pass functions as inputs to other functions, store functions in variables, and create flexible, reusable code. For example, you can pass a function handle to <code>integral</code> to compute integrals of different functions easily.

How do you create a function handle for the MATLAB function cos?

A f = function cos;

B f = cos();

C f = #cos;

D f = @cos;

Use the @ symbol followed by the function name without parentheses to create a function handle.

What does the following code do?
f = @(x) x + 5;

A Creates a function handle to multiply x by 5

B Calls a function named x + 5

C Creates a function handle to add 5 to input x

D Defines a variable x with value 5

The code defines an anonymous function that adds 5 to its input x and stores it in a function handle f.

How do you call a function handle f with input 10?

A f(10);

B call f with 10;

C f->10;

D f[10];

You call a function handle like a normal function using parentheses and passing the input.

Which of these is NOT a use of function handles?

A Passing functions as arguments

B Declaring variables of type integer

C Creating anonymous functions

D Storing functions in variables

Function handles are for referencing functions, not for declaring integer variables.

What will integral(@sin, 0, pi) do?

A Calculate the integral of sin(x) from 0 to pi

B Create a function handle named integral

C Return the sine of pi

D Cause an error because integral is not a function handle

The integral function takes a function handle and integration limits to compute the definite integral.

Explain what a function handle is in MATLAB and how you create one.

Think about how you refer to a function without calling it.

Describe how anonymous functions relate to function handles and give a simple example.

Anonymous functions are quick, one-line functions stored as handles.

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