Inheritance in MATLAB - Time & Space Complexity

Time Complexity: Inheritance

O(n)

Understanding Time Complexity

When using inheritance in MATLAB, it is important to understand how it affects the speed of your program.

We want to see how the time to run code changes as the input or object size grows.

Scenario Under Consideration

Analyze the time complexity of the following MATLAB class inheritance example.

classdef Animal
    methods
        function speak(obj)
            disp('Animal sound')
        end
    end
end

classdef Dog < Animal
    methods
        function speak(obj)
            disp('Bark')
        end
    end
end

% Create array of Dog objects and call speak
for i = 1:n
    d = Dog();
    d.speak();
end

This code defines a base class and a child class. It creates many Dog objects and calls a method on each.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The for-loop creating and calling speak() on each Dog object.
• How many times: The loop runs n times, once per Dog object.

How Execution Grows With Input

Each new Dog object requires creating the object and calling its method once.

Input Size (n)	Approx. Operations
10	About 10 object creations and method calls
100	About 100 object creations and method calls
1000	About 1000 object creations and method calls

Pattern observation: The work grows directly with the number of objects created.

Final Time Complexity

Time Complexity: O(n)

This means the time to run grows in a straight line as you create more objects and call their methods.

Common Mistake

[X] Wrong: "Inheritance makes the code slower exponentially because of extra layers."

[OK] Correct: Inheritance adds a small fixed overhead per method call, but the main time depends on how many objects and calls you make, not the inheritance depth.

Interview Connect

Understanding how inheritance affects time helps you write clear and efficient object-oriented code, a useful skill in many programming tasks.

Self-Check

What if we changed the loop to call a method that itself calls another inherited method? How would the time complexity change?

Practice

1. What does inheritance allow a subclass to do in MATLAB?

easy

A. Change MATLAB's built-in functions

B. Use properties and methods from a parent class

C. Run code without a main function

D. Create variables without declaring them

Solution

1. Step 1: Understand inheritance concept

   Inheritance means a subclass can use code from a parent class.

2. Step 2: Identify what subclass gains

   The subclass gets properties and methods from the parent class automatically.

3. Final Answer:

   Use properties and methods from a parent class -> Option B

4. Quick Check:

   Inheritance = reuse parent code [OK]

Hint: Inheritance means reuse parent class code [OK]

Common Mistakes:

• Thinking inheritance creates variables automatically
• Confusing inheritance with running code without main
• Believing inheritance changes built-in MATLAB functions

2. Which of the following is the correct way to declare a subclass Dog that inherits from superclass Animal in MATLAB?

easy

A. classdef Dog inherits Animal

B. classdef Dog : Animal

C. classdef Dog extends Animal

D. classdef Dog < Animal

Solution

1. Step 1: Recall MATLAB inheritance syntax

   MATLAB uses < symbol to indicate inheritance in classdef.

2. Step 2: Match correct syntax

   The correct syntax is classdef Dog < Animal.

3. Final Answer:

   classdef Dog < Animal -> Option D

4. Quick Check:

   Inheritance uses < in MATLAB [OK]

Hint: Use < to inherit in MATLAB classdef [OK]

Common Mistakes:

• Using 'inherits' keyword instead of <
• Using ':' or 'extends' which are not MATLAB syntax
• Confusing MATLAB syntax with other languages

3. Consider the following MATLAB code:

classdef Animal
    methods
        function sound(obj)
            disp('Some sound')
        end
    end
end

classdef Dog < Animal
    methods
        function sound(obj)
            disp('Bark')
        end
    end
end

myPet = Dog();
myPet.sound();

What will be the output when running myPet.sound()?

medium

A. Error: Method not found

B. Some sound

C. Bark

D. No output

Solution

1. Step 1: Understand method overriding in subclass

   The subclass Dog defines its own sound method, which replaces the superclass method.

2. Step 2: Determine which method runs

   Calling myPet.sound() runs the Dog version, printing 'Bark'.

3. Final Answer:

   Bark -> Option C

4. Quick Check:

   Subclass method overrides superclass method [OK]

Hint: Subclass method overrides superclass method [OK]

Common Mistakes:

• Expecting superclass method output
• Thinking both methods run
• Assuming error due to overriding

4. What is wrong with this MATLAB subclass definition?

classdef Cat <
    methods
        function meow(obj)
            disp('Meow')
        end
    end
end

medium

A. Missing superclass name after <

B. Method name cannot be 'meow'

C. Classdef keyword is misspelled

D. No constructor defined

Solution

1. Step 1: Check inheritance syntax

   The symbol < must be followed by the superclass name.

2. Step 2: Identify missing superclass

   Here, no superclass name is given after <, causing syntax error.

3. Final Answer:

   Missing superclass name after < -> Option A

4. Quick Check:

   Inheritance requires superclass name after < [OK]

Hint: Always specify superclass name after < [OK]

Common Mistakes:

• Leaving out superclass name after <
• Thinking method names cause error
• Assuming constructor is mandatory

5. You have a superclass Vehicle with a method move() that prints 'Moving'. You want to create a subclass Car that inherits Vehicle but adds a new method honk() that prints 'Beep!'. Which of the following is the correct MATLAB code for the subclass Car?

hard

A. classdef Car < Vehicle
methods
function honk(obj)
disp('Beep!')
end
end
end

B. classdef Car inherits Vehicle
methods
function honk(obj)
disp('Beep!')
end
end
end

C. classdef Car : Vehicle
methods
function honk(obj)
disp('Beep!')
end
end
end

D. classdef Car extends Vehicle
methods
function honk(obj)
disp('Beep!')
end
end
end

Solution

1. Step 1: Use correct inheritance syntax

   MATLAB uses < to inherit, so classdef Car < Vehicle is correct.

2. Step 2: Add new method in subclass

   The method honk is added inside methods block correctly.

3. Final Answer:

   classdef Car < Vehicle with honk method -> Option A

4. Quick Check:

   Subclass syntax + new method = classdef Car < Vehicle methods function honk(obj) disp('Beep!') end end end [OK]

Hint: Use < and add methods block for new methods [OK]

Common Mistakes:

• Using 'inherits', ':', or 'extends' instead of <
• Forgetting to add methods block
• Trying to override without correct syntax