Model hierarchy and navigation in Simulink - Mini Project: Build & Apply

Model hierarchy and navigation

📖 Scenario: You are working with a Simulink model that represents a simple control system. The model has multiple subsystems nested inside each other. You want to understand how to navigate through the model hierarchy and access specific blocks inside subsystems.

🎯 Goal: Learn how to create a Simulink model with nested subsystems, configure a variable to hold the current system path, navigate through the model hierarchy using commands, and display the names of blocks inside a selected subsystem.

📋 What You'll Learn

Create a Simulink model with nested subsystems

Define a variable to hold the current system path

Use commands to navigate the model hierarchy

List blocks inside a subsystem

Display the output of navigation

💡 Why This Matters

🌍 Real World

Engineers often work with complex Simulink models that have many nested subsystems. Navigating the model hierarchy helps them understand and modify parts of the system efficiently.

💼 Career

Knowing how to navigate and manipulate Simulink model hierarchies is essential for control system engineers, simulation specialists, and anyone working with model-based design.

1

Create a Simulink model with nested subsystems

Create a new Simulink model called control_system. Add a subsystem named Controller inside control_system. Inside Controller, add another subsystem named PID.

Simulink

% Your code here to create the model and subsystems

Hint

Use new_system to create the model and add_block to add subsystems with full path names.

2

Set current system path variable

Create a variable called current_system and set it to the path of the Controller subsystem inside control_system.

Simulink

control_system = 'control_system';
new_system(control_system);
open_system(control_system);
add_block('simulink/Ports & Subsystems/Subsystem', [control_system '/Controller']);
add_block('simulink/Ports & Subsystems/Subsystem', [control_system '/Controller/PID']);

% Set current_system to the Controller subsystem path
% Your code here

Hint

Use string concatenation or brackets to combine control_system and '/Controller'.

3

Navigate and list blocks inside the Controller subsystem

Use the variable current_system to get a list of all blocks inside the Controller subsystem. Store the list in a variable called blocks_in_controller.

Simulink

control_system = 'control_system';
new_system(control_system);
open_system(control_system);
add_block('simulink/Ports & Subsystems/Subsystem', [control_system '/Controller']);
add_block('simulink/Ports & Subsystems/Subsystem', [control_system '/Controller/PID']);

current_system = [control_system '/Controller'];

% Get blocks inside Controller subsystem
% Your code here

Hint

Use find_system with SearchDepth set to 1 and Type set to 'block'.

4

Display the blocks inside Controller subsystem

Print the variable blocks_in_controller to display the list of blocks inside the Controller subsystem.

Simulink

control_system = 'control_system';
new_system(control_system);
open_system(control_system);
add_block('simulink/Ports & Subsystems/Subsystem', [control_system '/Controller']);
add_block('simulink/Ports & Subsystems/Subsystem', [control_system '/Controller/PID']);

current_system = [control_system '/Controller'];

blocks_in_controller = find_system(current_system, 'SearchDepth', 1, 'Type', 'block');

% Print the blocks_in_controller variable
% Your code here

Hint

Use disp to print the message and the list variable.

Practice

1. What is the main purpose of using model hierarchy in Simulink?

easy

A. To automatically generate code from the model

B. To increase the simulation speed by skipping blocks

C. To break a large model into smaller, manageable parts

D. To change the color scheme of the model

Solution

1. Step 1: Understand model hierarchy concept

   Model hierarchy means dividing a big model into smaller parts called subsystems or referenced models.

2. Step 2: Identify the main benefit

   This division helps manage complexity and makes the model easier to understand and develop.

3. Final Answer:

   To break a large model into smaller, manageable parts -> Option C

4. Quick Check:

   Model hierarchy = smaller parts [OK]

Hint: Think 'big to small parts' for model hierarchy [OK]

Common Mistakes:

• Confusing hierarchy with simulation speed
• Thinking hierarchy changes model appearance
• Assuming hierarchy auto-generates code

2. Which Simulink command is used to open a subsystem from the current model window?

easy

A. open_system('subsystem_name')

B. close_system('subsystem_name')

C. save_system('subsystem_name')

D. run_system('subsystem_name')

Solution

1. Step 1: Recall command to open subsystems

   The command open_system('name') opens the specified subsystem or model window.

2. Step 2: Verify other commands

   close_system closes, save_system saves, and run_system runs simulations, not open.

3. Final Answer:

   open_system('subsystem_name') -> Option A

4. Quick Check:

   Open subsystem = open_system [OK]

Hint: Use open_system to open any model part [OK]

Common Mistakes:

• Using close_system to open models
• Confusing save_system with open_system
• Assuming run_system opens models

3. Given the following commands in Simulink:

open_system('topModel/subsystem1')
open_system('topModel/subsystem1/subsubsystemA')

What will be the result?

medium

A. Both subsystem1 and subsubsystemA windows open

B. Only subsystem1 window opens

C. Only subsubsystemA window opens

D. An error occurs because subsubsystemA is nested

Solution

1. Step 1: Understand open_system behavior

   Each open_system command opens the specified model or subsystem window independently.

2. Step 2: Analyze nested subsystem opening

   Calling open_system on a nested subsystem opens that window even if parent is already open.

3. Final Answer:

   Both subsystem1 and subsubsystemA windows open -> Option A

4. Quick Check:

   open_system opens each specified window [OK]

Hint: Each open_system call opens its target window [OK]

Common Mistakes:

• Thinking nested subsystems open automatically
• Assuming error on nested subsystem open
• Believing only one window opens at a time

4. You try to navigate to a subsystem using open_system('model//subsystem') but get an error. What is the likely cause?

medium

A. Subsystem does not exist in the model

B. Incorrect path syntax with double slashes

C. Model is not loaded in memory

D. open_system cannot open subsystems

Solution

1. Step 1: Check path syntax

   The path uses double slashes //, which is invalid in Simulink paths.

2. Step 2: Understand correct path format

   Paths should use single slashes / to separate model and subsystem names.

3. Final Answer:

   Incorrect path syntax with double slashes -> Option B

4. Quick Check:

   Use single slash in paths [OK]

Hint: Use single slash '/' in subsystem paths [OK]

Common Mistakes:

• Using double slashes in paths
• Assuming open_system can't open subsystems
• Ignoring model load status

5. You have a large Simulink model with many nested subsystems. To improve navigation and clarity, which approach is best?

hard

A. Use only one big subsystem without nesting

B. Flatten all subsystems into one level to avoid hierarchy

C. Disable hierarchy navigation commands

D. Use model referencing to separate parts into independent models

Solution

1. Step 1: Understand model referencing benefits

   Model referencing breaks large models into separate files, improving clarity and reusability.

2. Step 2: Compare alternatives

   Flattening or using one big subsystem reduces clarity and manageability; disabling navigation removes helpful tools.

3. Final Answer:

   Use model referencing to separate parts into independent models -> Option D

4. Quick Check:

   Model referencing = better clarity and navigation [OK]

Hint: Use model referencing for big, nested models [OK]

Common Mistakes:

• Flattening hierarchy reduces clarity
• Using one big subsystem is hard to manage
• Disabling navigation commands hurts workflow