Hardware-in-the-loop (HIL) testing concept in Simulink - Time & Space Complexity

Time Complexity: Hardware-in-the-loop (HIL) testing concept

O(numTests)

Understanding Time Complexity

When using Hardware-in-the-loop (HIL) testing in Simulink, it is important to understand how the time to run tests changes as the system or model grows.

We want to know how the testing time increases when the model or hardware setup becomes more complex.

Scenario Under Consideration

Analyze the time complexity of the following Simulink HIL testing setup.

% Simulink HIL test loop example
for i = 1:numTests
    % Load model
    load_system('plant_model');
    % Configure HIL interface
    hil = hil_initialize();
    % Run simulation with hardware
    simOut = sim('plant_model');
    % Collect results
    results(i) = process_output(simOut);
    % Close model
    close_system('plant_model', 0);
end
    

This code runs multiple HIL tests by loading the model, running simulation with hardware, and collecting results each time.

Identify Repeating Operations

Look at what repeats in the code.

• Primary operation: The for-loop runs the entire test sequence multiple times.
• How many times: It runs once for each test, so numTests times.
• Inside the loop, loading and closing the model happen every time, which are costly operations.

How Execution Grows With Input

As the number of tests increases, the total time grows roughly in direct proportion.

Input Size (numTests)	Approx. Operations
10	10 full test runs
100	100 full test runs
1000	1000 full test runs

Pattern observation: Doubling the number of tests doubles the total execution time.

Final Time Complexity

Time Complexity: O(numTests)

This means the total testing time grows linearly with the number of tests you run.

Common Mistake

[X] Wrong: "Loading the model once means the loop runs in constant time regardless of test count."

[OK] Correct: In this setup, the model loads and closes inside the loop, so each test adds time. The total time grows with the number of tests.

Interview Connect

Understanding how test time grows with test count helps you design efficient HIL testing workflows and shows you can analyze real system performance.

Self-Check

What if we moved the model loading and closing outside the loop? How would the time complexity change?