Relational expressions in MATLAB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a relational expression in MATLAB?

A relational expression compares two values or arrays and returns a logical array of true (1) or false (0) depending on the comparison.

beginner

Which symbol is used for 'greater than or equal to' in MATLAB?

The symbol '>=' is used for 'greater than or equal to' in MATLAB.

beginner

What is the result of the expression: 5 < 3 in MATLAB?

The result is logical 0 (false) because 5 is not less than 3.

intermediate

How does MATLAB handle relational expressions with arrays?

MATLAB compares each element of the arrays element-wise and returns a logical array of the same size with true or false values.

beginner

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

'==' is a relational operator used to test equality, returning true or false. '=' is an assignment operator used to assign values to variables.

What does the relational operator '<=' mean in MATLAB?

A Less than or equal to

B Greater than or equal to

C Equal to

D Not equal to

The operator '<=' means 'less than or equal to' in MATLAB.

What is the output of the expression: [1 3 5] > 3 in MATLAB?

A [0 1 1]

B [1 1 1]

C [0 0 1]

D [1 0 0]

Each element is compared to 3: 1>3 is false (0), 3>3 is false (0), 5>3 is true (1).

Which relational operator checks if two values are not equal in MATLAB?

A ~=

B ==

C !=

D =

The operator '~=' means 'not equal to' in MATLAB.

What type of value does a relational expression return in MATLAB?

A String value

B Logical value (true or false)

C Numeric value

D Character array

Relational expressions return logical values: true (1) or false (0).

What happens if you compare two arrays of different sizes using relational operators in MATLAB?

A MATLAB compares element-wise ignoring extra elements

B MATLAB automatically resizes arrays

C MATLAB returns a scalar logical value

D MATLAB returns an error

MATLAB requires arrays to be the same size or compatible for element-wise comparison; otherwise, it returns an error.

Explain what relational expressions are in MATLAB and how they are used with arrays.

Think about how MATLAB compares numbers or arrays and what kind of result it gives.

List the common relational operators in MATLAB and describe what each one does.

Focus on the symbols and their meanings for comparing values.

Practice

1. Which of the following relational operators in MATLAB checks if two values are NOT equal?

easy

A. ==

B. <=

C. >=

D. ~=

Solution

1. Step 1: Understand the meaning of relational operators

   The operator == checks equality, ~= checks inequality, and >=, <= check greater or equal and less or equal respectively.

2. Step 2: Identify the operator for NOT equal

   The operator ~= means NOT equal in MATLAB.

3. Final Answer:

   ~= -> Option D

4. Quick Check:

   NOT equal operator = ~= [OK]

Hint: Remember: ~= means NOT equal in MATLAB [OK]

Common Mistakes:

• Confusing == with ~=
• Using = instead of ==
• Mixing up >= and >

2. Which of the following is the correct syntax to check if variable a is greater than or equal to 10 in MATLAB?

easy

A. a >== 10

B. a >= 10

C. a =< 10

D. a => 10

Solution

1. Step 1: Recall MATLAB relational operator syntax

   MATLAB uses >= to mean greater than or equal to.

2. Step 2: Check each option for correct syntax

   a >= 10 uses >= correctly. Options A, B, and C use invalid or reversed operators.

3. Final Answer:

   a >= 10 -> Option B

4. Quick Check:

   Greater or equal operator = >= [OK]

Hint: Use >= for greater or equal, not => or =< [OK]

Common Mistakes:

• Writing => instead of >=
• Writing =< instead of <=
• Adding extra = signs

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

a = 5; b = 7;
result = (a < b) & (b <= 7);
disp(result);

medium

A. 1

B. 0

C. Error

D. [1 0]

Solution

1. Step 1: Evaluate each relational expression

   a < b is 5 < 7 which is true (1). b <= 7 is 7 <= 7 which is true (1).

2. Step 2: Apply logical AND operator &

   Both expressions are true, so (1 & 1) equals 1 (true).

3. Final Answer:

   1 -> Option A

4. Quick Check:

   True & True = 1 [OK]

Hint: True & True gives 1, false & anything gives 0 [OK]

Common Mistakes:

• Confusing & with &&
• Expecting output as logical word instead of 1
• Misreading <= operator

4. Identify the error in this MATLAB code snippet:

x = 10;
if x = 10
    disp('Equal to 10');
end

medium

A. Using = instead of == in if condition

B. Missing semicolon after disp statement

C. Incorrect use of end keyword

D. Variable x is not initialized

Solution

1. Step 1: Check the if condition syntax

   In MATLAB, = is assignment, == is comparison. Using = in if causes error.

2. Step 2: Confirm other parts are correct

   Semicolon after disp is optional, end is correctly used, x is initialized.

3. Final Answer:

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

4. Quick Check:

   Comparison needs ==, not = [OK]

Hint: Use == for comparison inside if, not = [OK]

Common Mistakes:

• Using = instead of ==
• Thinking semicolon is mandatory after disp
• Misplacing end keyword

5. Given a vector v = [3, 6, 9, 12], which MATLAB expression returns a logical array indicating elements greater than 5 and less than or equal to 10?

hard

A. v > (5 & v) <= 10

B. v > 5 && v <= 10

C. (v > 5) & (v <= 10)

D. (v > 5) | (v <= 10)

Solution

1. Step 1: Understand vector relational operations

   Relational operators applied to vectors return logical arrays element-wise.

2. Step 2: Combine conditions correctly with parentheses and &

   Use parentheses around each condition: (v > 5) & (v <= 10) to get elements satisfying both.

3. Step 3: Check other options for syntax errors

   v > 5 && v <= 10 uses short-circuit &&, invalid for vectors. v > (5 & v) <= 10 is invalid syntax. (v > 5) | (v <= 10) uses OR instead of AND.

4. Final Answer:

   (v > 5) & (v <= 10) -> Option C

5. Quick Check:

   Use parentheses with & for combined conditions [OK]

Hint: Always use parentheses around each relational condition [OK]

Common Mistakes:

• Using && instead of & for array operations
• Using | instead of & for AND
• Writing invalid combined expressions