Model hierarchy and navigation in Simulink - Step-by-Step Execution

Concept Flow - Model hierarchy and navigation

Open top-level model

↓

View model blocks

↓

Identify subsystem block

↓

Double-click subsystem

↓

Open subsystem model

↓

Repeat navigation or return

↓

Close subsystem or top-level model

This flow shows how you start from a top-level Simulink model, identify subsystems, and navigate inside them by opening their detailed views, then return or close models.

Execution Sample

Simulink

open_system('top_model')
find_system('top_model','BlockType','SubSystem')
open_system('top_model/subsystem1')
close_system('top_model/subsystem1')
close_system('top_model')

This code opens a top-level model, finds subsystems, opens one subsystem, then closes it and the top model.

Execution Table

Step	Action	Model/Block	Result/State
1	open_system	'top_model'	Top-level model window opens
2	find_system	'top_model', BlockType='SubSystem'	List of subsystems found: ['subsystem1', 'subsystem2']
3	open_system	'top_model/subsystem1'	Subsystem1 window opens inside top_model
4	close_system	'top_model/subsystem1'	Subsystem1 window closes
5	close_system	'top_model'	Top-level model window closes

💡 All opened models closed, navigation session ends

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
open_models	[]	['top_model']	['top_model', 'top_model/subsystem1']	['top_model']	[]
found_subsystems	[]	['subsystem1', 'subsystem2']	['subsystem1', 'subsystem2']	['subsystem1', 'subsystem2']	['subsystem1', 'subsystem2']

Key Moments - 2 Insights

Why do we need to open a subsystem separately after finding it?

Finding a subsystem lists its name but does not open its detailed view. Opening it lets you see and edit inside that subsystem, as shown in step 3 of the execution_table.

What happens if we close the top-level model before closing subsystems?

Closing the top-level model automatically closes all its open subsystems. The execution_table shows closing subsystems first is cleaner but not mandatory.

Visual Quiz - 3 Questions

Look at the execution_table, what is the state of open_models after step 3?

A []

B ['top_model']

C ['top_model', 'top_model/subsystem1']

D ['top_model/subsystem1']

💡 Hint

Check the variable_tracker row for open_models after step 3

At which step does the subsystem window close?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Look at the action column in execution_table for 'close_system' on subsystem

If we skip step 3 and try to close 'top_model/subsystem1' directly, what happens?

A Subsystem closes successfully

B Error because subsystem is not open

C Top-level model closes instead

D Nothing happens

💡 Hint

Subsystem must be open before closing; check open_models variable in variable_tracker

Concept Snapshot

Model hierarchy in Simulink means models contain subsystems.
Navigate by opening top model, then double-click subsystems to open.
Use open_system() and close_system() commands to manage views.
Subsystems must be opened before editing or closing.
Closing top model closes all open subsystems automatically.

Full Transcript

In Simulink, models are organized in a hierarchy where a top-level model contains subsystems. To navigate, you first open the top-level model window. Then you identify subsystems inside it. To see inside a subsystem, you open it separately. You can repeat this to go deeper or return to higher levels. When done, close subsystems and the top model to end the session. This process helps manage complex models by focusing on parts step-by-step.

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