Relational expressions in MATLAB - Step-by-Step Execution

Concept Flow - Relational expressions

Start with two values

↓

Apply relational operator

↓

Evaluate condition: true or false

↓

Use result in program

↓

End

Relational expressions compare two values and return true (1) or false (0) based on the condition.

Execution Sample

MATLAB

a = 5;
b = 3;
c = a > b;

Compare if a is greater than b and store the result in c.

Execution Table

Step	Expression	Evaluation	Result
1	a = 5	Assign 5 to a	a = 5
2	b = 3	Assign 3 to b	b = 3
3	a > b	Is 5 greater than 3?	true (1)
4	c = a > b	Store result of comparison in c	c = 1

💡 All expressions evaluated; relational comparison completed.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 4
a	undefined	5	5	5
b	undefined	undefined	3	3
c	undefined	undefined	undefined	1

Key Moments - 2 Insights

Why does the relational expression return 1 or 0 instead of true or false words?

In MATLAB, relational expressions return numeric logical values: 1 for true and 0 for false, as shown in execution_table step 3 and 4.

What happens if both sides of the relational operator are equal?

The expression evaluates to 0 (false) for '>' operator, because 5 > 5 is false. This is shown in the evaluation logic in execution_table.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the result of 'a > b'?

A 5

B 0 (false)

C 1 (true)

D 3

💡 Hint

Check the 'Result' column in execution_table row 3.

At which step is the variable 'c' assigned a value?

A Step 1

B Step 4

C Step 3

D Step 2

💡 Hint

Look at the 'Expression' and 'Result' columns in execution_table.

If 'a' was 2 and 'b' was 3, what would be the result of 'a > b'?

A 0

B 1

C 2

D 3

💡 Hint

Relational expressions return 1 if true, 0 if false; 2 > 3 is false.

Concept Snapshot

Relational expressions compare two values using operators like >, <, ==.
They return 1 (true) or 0 (false) in MATLAB.
Example: c = a > b;
Assigns 1 to c if a is greater than b, else 0.
Used for decision making and conditions.

Full Transcript

Relational expressions in MATLAB compare two values and return 1 for true or 0 for false. For example, if a equals 5 and b equals 3, the expression a > b evaluates to 1 because 5 is greater than 3. Variables store these results for use in programs. This process helps programs make decisions based on conditions.

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