Function handles in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple function handle call

What is the output of this MATLAB code?

MATLAB

f = @(x) x^2 + 3*x + 1;
result = f(2);
disp(result);

A 15

B 9

C 7

D 11

💡 Hint

Calculate 2 squared plus 3 times 2 plus 1.

The function computes x^2 + 3*x + 1. For x=2, 2^2=4, 3*2=6, sum is 4+6+1=11.

❓ Predict Output

intermediate

Function handle with multiple inputs

What is the output of this MATLAB code?

MATLAB

g = @(x,y) x*y + y^2;
val = g(3,4);
disp(val);

A 28

B 19

C 25

D 16

💡 Hint

Calculate 3*4 + 4^2.

g(3,4) = 3*4 + 4^2 = 12 + 16 = 28.

🔧 Debug

advanced

Identify the error in function handle usage

What error does this MATLAB code produce?

MATLAB

h = @(x) x(2) + 5;
result = h(3);
disp(result);

A Undefined function or variable 'x'.

B Index exceeds matrix dimensions.

C Syntax error: missing operator.

D No error, output is 8.

💡 Hint

Check how x is used inside the function handle.

The function tries to access the second element of x, but x is a scalar (3), so indexing fails.

🧠 Conceptual

advanced

Function handle behavior with variable scope

Consider this MATLAB code snippet. What is the output?

MATLAB

a = 10;
f = @(x) x + a;
a = 20;
disp(f(5));

A 15

B Error: Undefined variable 'a'.

C 25

D 5

💡 Hint

Anonymous functions in MATLAB capture variables by value at the time of creation.

When the function handle is created, a=10 is captured. Changing a to 20 afterward does not affect the function. Thus, f(5) = 5 + 10 = 15.

❓ Predict Output

expert

Output of nested function handles with array input

What is the output of this MATLAB code?

MATLAB

f1 = @(x) x.^2;
f2 = @(g, y) g(y) + 1;
arr = [1, 2, 3];
result = f2(f1, arr);
disp(result);

A [1 4 9]

B [2 4 6]

C [2 5 10]

D Error: Matrix dimensions must agree.

💡 Hint

Apply f1 to each element of arr, then add 1 to each result.

f1 squares each element: [1 4 9]. Adding 1 gives [2 5 10].

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