Logical values in MATLAB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are logical values in MATLAB?

Logical values in MATLAB represent true or false states, stored as 1 (true) or 0 (false). They are used for decision making and conditions.

beginner

How do you create a logical true and false in MATLAB?

You can create logical true with true or 1, and logical false with false or 0. For example, a = true; and b = false;.

intermediate

What is the output of logical(5) in MATLAB?

The output is 1 (true) because any nonzero number converts to logical true.

intermediate

How can logical values be used in MATLAB indexing?

Logical values can index arrays by selecting elements where the logical array is true. For example, A([true false true]) returns the 1st and 3rd elements of A.

beginner

What is the difference between == and = in MATLAB?

= is used to assign values to variables, while == tests equality and returns logical true or false.

What does the expression logical(0) return in MATLAB?

A 0 (false)

B 1 (true)

C Error

D NaN

logical(0) returns 0, which means false.

Which of these is a logical true value in MATLAB?

A false

B 1

C 0

D -1

In MATLAB, 1 represents logical true.

What will A([true false true]) do if A = [10 20 30]?

A [10 30]

B [10 20 30]

C [20]

D Error

The logical index selects the 1st and 3rd elements, so output is [10 30].

What is the result of 5 == 5 in MATLAB?

A 5

B false

C Error

D true

5 == 5 tests equality and returns logical true.

Which operator assigns a value to a variable in MATLAB?

A ==

B &&

C =

D ~=

= is the assignment operator.

Explain what logical values are in MATLAB and how they are used.

Think about how computers decide yes/no or on/off.

Describe how logical indexing works with an example in MATLAB.

Imagine using a filter to pick certain items.

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