Logical values in MATLAB - Mini Project: Build & Apply

Logical values

📖 Scenario: Imagine you are working with a list of temperatures recorded over a week. You want to find out which days were hot, meaning the temperature was above 30 degrees Celsius.

🎯 Goal: You will create a logical array that shows true for days with temperatures above 30 and false otherwise.

📋 What You'll Learn

Create a variable called temperatures with the exact values: [28, 31, 29, 35, 27, 33, 30]

Create a variable called threshold and set it to 30

Create a logical array called isHot that is true where temperatures are greater than threshold

Display the isHot array using disp

💡 Why This Matters

🌍 Real World

Logical arrays are useful to filter data, such as finding days with high temperatures or selecting items that meet certain conditions.

💼 Career

Understanding logical values is important for data analysis, engineering, and scientific computing jobs where decision-making based on conditions is common.

1

Create the temperature data

Create a variable called temperatures and assign it the array [28, 31, 29, 35, 27, 33, 30].

MATLAB

% Create the temperatures array
% Your code here

Hint

Use square brackets [] to create an array in MATLAB.

2

Set the temperature threshold

Create a variable called threshold and set it to 30.

MATLAB

temperatures = [28, 31, 29, 35, 27, 33, 30];
% Create the threshold variable
% Your code here

Hint

Just assign the number 30 to the variable threshold.

3

Create the logical array

Create a logical array called isHot that is true where temperatures are greater than threshold.

MATLAB

temperatures = [28, 31, 29, 35, 27, 33, 30];
threshold = 30;
% Create the logical array isHot
% Your code here

Hint

Use the greater than operator > to compare each temperature to the threshold.

4

Display the logical array

Use disp to display the isHot array.

MATLAB

temperatures = [28, 31, 29, 35, 27, 33, 30];
threshold = 30;
isHot = temperatures > threshold;
% Display the isHot array
% Your code here

Hint

Use disp(isHot) to show the logical array in the command window.

Practice

1. What is the result of the expression 5 > 3 in MATLAB?

easy

A. 5

B. false

C. 3

D. true

Solution

1. Step 1: Understand the comparison operator

   The operator > checks if the left number is greater than the right number.

2. Step 2: Compare the numbers 5 and 3

   Since 5 is greater than 3, the expression returns true.

3. Final Answer:

   true -> Option D

4. Quick Check:

   5 > 3 = true [OK]

Hint: Greater than means left number bigger than right [OK]

Common Mistakes:

• Confusing true with the number 5
• Thinking it returns the bigger number
• Mixing up > and < operators

2. Which of the following is the correct way to create a logical true value in MATLAB?

easy

A. 1 == 1

B. 1 = 1

C. logical(0)

D. true

Solution

1. Step 1: Evaluate each option

   logical(0) returns false.
   1 = 1 causes syntax error (cannot assign to constant).
   true errors (function requires arguments like true()).
   1 == 1 returns true.

2. Step 2: Identify the working method

   Only 1 == 1 correctly creates a logical true value.

3. Final Answer:

   1 == 1 -> Option A

4. Quick Check:

   1 == 1 = true [OK]

Hint: Use == in comparisons to get logical true [OK]

Common Mistakes:

• logical(0) returns false
• Using = instead of == for comparison
• Omitting () on true()

3. What is the output of this MATLAB code?

val = (4 < 2) | (7 == 7);
disp(val);

medium

A. Error

B. 0

C. 1

D. [0 1]

Solution

1. Step 1: Evaluate each logical expression

   4 < 2 is false (0), 7 == 7 is true (1).

2. Step 2: Apply the OR operator (|)

   False OR True results in true (1).

3. Final Answer:

   1 -> Option C

4. Quick Check:

   (false OR true) = true = 1 [OK]

Hint: OR is true if any side is true [OK]

Common Mistakes:

• Confusing OR (|) with AND (&)
• Expecting vector output
• Misreading comparison operators

4. Identify the error in this MATLAB code:

if 5 = 5
    disp('Equal');
end

medium

A. Using single = instead of == in if condition

B. Missing semicolon after disp statement

C. Incorrect use of disp function

D. No error, code runs fine

Solution

1. Step 1: Check the if condition syntax

   The single equal sign = is for assignment, not comparison.

2. Step 2: Correct the comparison operator

   Use double equal signs == to compare values in conditions.

3. Final Answer:

   Using single = instead of == in if condition -> Option A

4. Quick Check:

   Comparison needs ==, not = [OK]

Hint: Use == for comparison, = for assignment [OK]

Common Mistakes:

• Using = in if condition
• Ignoring MATLAB error messages
• Assuming semicolon is mandatory after disp

5. Given the vector A = [-1 0 1 2 0], which MATLAB expression returns a logical vector indicating which elements are nonzero?

hard

A. All of the above

B. A ~= 0

C. A > 0

D. A != 0

Solution

1. Step 1: Understand each expression

   A ~= 0 returns true where not zero.
   A != 0 uses invalid != operator (use ~=).
   A > 0 true only for positives.

2. Step 2: Check which elements each marks true for A = [-1 0 1 2 0]

   - A ~= 0: [true, false, true, true, false]
   - A != 0: syntax error
   - A > 0: [false, false, true, true, false]

3. Final Answer:

   A ~= 0 -> Option B

4. Quick Check:

   A ~= 0 = nonzero logical vector [OK]

Hint: Use ~= 0 to find nonzero elements [OK]

Common Mistakes:

• Using != instead of ~=
• Confusing ~= with ==
• Assuming >0 misses negative nonzero