Variant subsystems in Simulink - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a variant subsystem block in Simulink.

Simulink

variantBlock = add_block('simulink/Ports & Subsystems/Variant Subsystem', '[1]');

Drag options to blanks, or click blank then click option'

A'myModel/Constant'

B'myModel/VariantSubsystem'

C'myModel/Sum'

D'myModel/Gain'

Attempts:

3 left

💡 Hint

Common Mistakes

Using a block path that does not include the model name.

Using a block type instead of a block path.

The correct path specifies the location and name of the variant subsystem block in the model.

2fill in blank

medium

Complete the code to set the variant control variable for the subsystem.

Simulink

set_param('[1]', 'VariantControl', 'mode');

Drag options to blanks, or click blank then click option'

A'myModel/VariantSubsystem'

B'myModel/Constant'

C'myModel/Sum'

D'myModel/Gain'

Attempts:

3 left

💡 Hint

Common Mistakes

Setting the parameter on a non-variant block.

Using an incorrect block path.

The variant control variable is set on the variant subsystem block to control which variant is active.

3fill in blank

hard

Fix the error in the code to activate the correct variant based on the control variable.

Simulink

variantControl = [1];
set_param('myModel/VariantSubsystem', 'VariantControl', variantControl);

Drag options to blanks, or click blank then click option'

A'mode1'

Bmode1

C'variant1'

Dvariant1

Attempts:

3 left

💡 Hint

Common Mistakes

Not using quotes around the variant control string.

Using an undefined variable instead of a string.

The variant control variable must be a string, so it needs to be enclosed in quotes.

4fill in blank

hard

Fill both blanks to create a variant condition and assign it to a variant choice block.

Simulink

variantChoice = add_block('simulink/Ports & Subsystems/Variant Choice', '[1]');
set_param(variantChoice, 'VariantCondition', '[2]');

Drag options to blanks, or click blank then click option'

A'myModel/VariantChoice'

B'mode == 1'

C'mode == 2'

D'myModel/VariantSubsystem'

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong block path for the variant choice block.

Setting an incorrect or invalid variant condition.

The variant choice block is added at the specified path, and the variant condition is set to 'mode == 1' to activate this choice when mode equals 1.

5fill in blank

hard

Fill all three blanks to create a variant switch and set its control variable and condition.

Simulink

variantSwitch = add_block('[1]', '[2]');
set_param(variantSwitch, 'VariantControl', '[3]');

Drag options to blanks, or click blank then click option'

Asimulink/Ports & Subsystems/Variant Subsystem

B'myModel/VariantSwitch'

C'mode'

Dsimulink/Ports & Subsystems/Variant Switch

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong block type path.

Not setting the variant control variable correctly.

The variant switch block is added at the specified path, and its variant control variable is set to 'mode' to control which variant is active.

Practice

1. What is the main purpose of a Variant Subsystem in Simulink?

easy

A. To generate code from a Simulink model

B. To switch between different subsystem implementations within one model

C. To create a new Simulink model automatically

D. To visualize simulation results in real-time

Solution

1. Step 1: Understand Variant Subsystem concept

   A Variant Subsystem allows multiple subsystem options inside one model but only runs one at a time.

2. Step 2: Identify the main purpose

   This helps switch between different designs easily without changing the whole model.

3. Final Answer:

   To switch between different subsystem implementations within one model -> Option B

4. Quick Check:

   Variant Subsystem = Switch subsystems [OK]

Hint: Variant subsystems let you pick one design option inside one model [OK]

Common Mistakes:

• Thinking it creates new models
• Confusing with code generation
• Assuming it visualizes results

2. Which of the following is the correct way to define a variant control variable in Simulink for a Variant Subsystem?

easy

A. variantControl -> 1; % Use arrow operator

B. variantControl == 1; % Use double equals for assignment

C. variantControl := 1; % Use colon equals operator

D. variantControl = 1; % Define control variable in MATLAB workspace

Solution

1. Step 1: Recall MATLAB syntax for variable assignment

   In MATLAB, variables are assigned using a single equals sign, e.g., var = value;.

2. Step 2: Identify correct syntax for variant control variable

   variantControl = 1; % Define control variable in MATLAB workspace uses = correctly. Options A, B, and C use invalid assignment operators.

3. Final Answer:

   variantControl = 1; % Define control variable in MATLAB workspace -> Option D

4. Quick Check:

   Assignment uses =, not == or := [OK]

Hint: Use single = for assignment in MATLAB workspace [OK]

Common Mistakes:

• Using == instead of = for assignment
• Using := or -> which are invalid in MATLAB
• Confusing control variable with variant condition

3. Given the following variant control variable and conditions:
variantControl = 2;
Which subsystem will run if the variant conditions are:
Subsystem A: variantControl == 1
Subsystem B: variantControl == 2
Subsystem C: variantControl == 3

medium

A. Subsystem B

B. Subsystem A

C. Subsystem C

D. No subsystem runs

Solution

1. Step 1: Check the value of variantControl

   The variable variantControl is set to 2.

2. Step 2: Match variantControl with subsystem conditions

   Subsystem B runs when variantControl == 2, which matches the current value.

3. Final Answer:

   Subsystem B -> Option A

4. Quick Check:

   variantControl 2 matches Subsystem B condition [OK]

Hint: Match variantControl value to condition to find active subsystem [OK]

Common Mistakes:

• Choosing subsystem A or C without matching condition
• Assuming multiple subsystems run simultaneously
• Ignoring exact equality in conditions

4. You have a Variant Subsystem with two variants controlled by variantControl. The control variable is set as variantControl = '1'; (a string). The variant conditions are variantControl == 1 and variantControl == 2. What error will occur?

medium

A. Error due to type mismatch between string and number

B. No error, Subsystem 2 runs

C. No error, Subsystem 1 runs

D. Error because variantControl is undefined

Solution

1. Step 1: Identify data types of variantControl and conditions

   variantControl is a string ('1'), but conditions compare to numbers (1 and 2).

2. Step 2: Understand type mismatch impact

   Comparing string to number with == causes a type mismatch error in Simulink variant evaluation.

3. Final Answer:

   Error due to type mismatch between string and number -> Option A

4. Quick Check:

   String vs number comparison causes error [OK]

Hint: Ensure variantControl type matches condition type to avoid errors [OK]

Common Mistakes:

• Assuming string '1' equals number 1
• Ignoring data type in variant conditions
• Thinking variantControl can be undefined

5. You want to compare two design options in a Simulink model using Variant Subsystems. One subsystem uses a PID controller, and the other uses a state-space controller. How should you set up the variant control variable and conditions to switch between these controllers during simulation?

hard

A. Set variantControl = true; for PID and variantControl = false; for state-space, then use conditions variantControl == true and variantControl == false

B. Use variantControl = 'PID'; and variantControl = 'StateSpace'; with conditions variantControl == 'PID' and variantControl == 'StateSpace'

C. Set variantControl = 1; for PID and variantControl = 2; for state-space, then use conditions variantControl == 1 and variantControl == 2 respectively

D. Use no variant control variable and manually enable one subsystem at a time

Solution

1. Step 1: Choose numeric variant control variable for clarity

   Using numeric values like 1 and 2 is simple and avoids type mismatch.

2. Step 2: Define variant conditions matching control variable values

   Conditions variantControl == 1 and variantControl == 2 clearly select PID or state-space subsystems.

3. Step 3: Avoid string or boolean variants for better compatibility

   Strings or booleans can cause errors or confusion in variant evaluation.

4. Final Answer:

   Set variantControl = 1 for PID and variantControl = 2 for state-space, with matching conditions -> Option C

5. Quick Check:

   Numeric control variable with matching conditions is best practice [OK]

Hint: Use numeric variantControl and matching == conditions for easy switching [OK]

Common Mistakes:

• Using strings causing type mismatch
• Using booleans which limit options
• Not using variantControl and enabling subsystems manually