Why Simulink models dynamic systems in MATLAB - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a Simulink model named 'myModel'.

MATLAB

model = [1]('myModel');

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

Anew_system

Bsimulink

Copen_system

Dadd_block

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'simulink' instead of 'new_system' creates an error.

Using 'open_system' opens an existing model, not create a new one.

The new_system function creates a new Simulink model with the specified name.

2fill in blank

medium

Complete the code to add a Gain block to the model 'myModel'.

MATLAB

add_block('simulink/Math Operations/Gain', '[1]/Gain');

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

AmyModel

Bsystem

Cmodel

Dblock

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'model' instead of the actual model name string.

Using 'system' or 'block' which are not model names.

The block path requires the model name as the parent system, here 'myModel'.

3fill in blank

hard

Fix the error in the code to set the Gain value to 5.

MATLAB

set_param('[1]/Gain', 'Gain', '5');

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

AGainBlock

BGain

Cmodel

DmyModel

Attempts:

3 left

💡 Hint

Common Mistakes

Using only the block name without the model prefix causes errors.

Using variable names that are not strings or do not match the model name.

The full path to the block requires the model name, here 'myModel', followed by the block name.

4fill in blank

hard

Fill both blanks to connect the output of the Gain block to the input of a Scope block.

MATLAB

add_block('simulink/Sinks/Scope', '[1]/Scope');
add_line('[2]', 'Gain/1', 'Scope/1');

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

AmyModel

Bmodel

Csystem

Dblock

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the two blanks causes errors.

Using variable names that are not the model name string.

Both the block addition and line connection require the model name 'myModel' as the system.

5fill in blank

hard

Fill all three blanks to save, open, and simulate the model 'myModel'.

MATLAB

save_system('[1]');
open_system('[2]');
sim('[3]');

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

Amodel

BmyModel

Csystem

Dblock

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for each function causes errors.

Using variable names that are not the model name string.

All three functions require the model name 'myModel' as the argument to operate on the correct model.

Practice

1. Why does Simulink model dynamic systems instead of static ones?

easy

A. Because Simulink only works with electrical circuits

B. Because static systems cannot be represented with blocks

C. Because dynamic systems do not require any input signals

D. Because dynamic systems change over time and need simulation to understand behavior

Solution

1. Step 1: Understand what dynamic systems are

   Dynamic systems are those that change their state over time, unlike static systems which remain constant.

2. Step 2: Recognize Simulink's purpose

   Simulink is designed to simulate and analyze systems that evolve over time, helping us predict their behavior.

3. Final Answer:

   Because dynamic systems change over time and need simulation to understand behavior -> Option D

4. Quick Check:

   Dynamic systems need simulation = Because dynamic systems change over time and need simulation to understand behavior [OK]

Hint: Dynamic means changing over time; Simulink simulates that [OK]

Common Mistakes:

• Confusing static with dynamic systems
• Thinking Simulink only models circuits
• Believing dynamic systems don't need inputs

2. Which of the following is the correct way to start a Simulink model in MATLAB?

easy

A. sim('modelname')

B. run('modelname')

C. start('modelname')

D. open('modelname')

Solution

1. Step 1: Recall the MATLAB command to run Simulink models

   The command sim('modelname') runs the Simulink model named 'modelname'.

2. Step 2: Understand other commands

   run is for scripts, start is not a MATLAB command for models, and open opens the model but does not run it.

3. Final Answer:

   sim('modelname') -> Option A

4. Quick Check:

   Run Simulink model = sim('modelname') [OK]

Hint: Use sim() to run models, open() just opens them [OK]

Common Mistakes:

• Using run() instead of sim()
• Confusing open() with run()
• Trying start() which is invalid

3. Given this Simulink model code snippet in MATLAB:

simOut = sim('simple_model');
y = simOut.get('yout');
disp(y(end));

What does disp(y(end)) display?

medium

A. The first output value of the simulation

B. The total simulation time

C. The last output value of the simulation

D. An error because yout is not defined

Solution

1. Step 1: Understand the code snippet

   The code runs a Simulink model named 'simple_model' and stores output in simOut. Then it extracts the output signal 'yout' into y.

2. Step 2: Analyze disp(y(end))

   The end keyword in MATLAB means the last element of the array y, so it displays the last output value from the simulation.

3. Final Answer:

   The last output value of the simulation -> Option C

4. Quick Check:

   y(end) = last output value [OK]

Hint: end means last element in MATLAB arrays [OK]

Common Mistakes:

• Thinking y(end) is the first value
• Confusing output value with simulation time
• Assuming yout is undefined causing error

4. You wrote this MATLAB code to simulate a Simulink model:

simOut = sim('myModel');
y = simOut.yout;
plot(y);

But MATLAB shows an error: Reference to non-existent field 'yout'. What is the likely fix?

medium

A. Use y = simOut.get('yout'); instead of direct field access

B. Change sim('myModel') to run('myModel')

C. Add yout as a variable in the base workspace

D. Restart MATLAB to clear the error

Solution

1. Step 1: Understand the error

   The error means simOut does not have a direct field named 'yout'. Simulink simulation outputs are accessed via the get() method.

2. Step 2: Correct the access method

   Using simOut.get('yout') properly retrieves the output signal from the simulation results.

3. Final Answer:

   Use y = simOut.get('yout'); instead of direct field access -> Option A

4. Quick Check:

   Use get() to access outputs [OK]

Hint: Use get('yout') to access simulation outputs [OK]

Common Mistakes:

• Trying to access yout as a field directly
• Using run() instead of sim()
• Ignoring the error and continuing

5. You want to model a heating system that changes temperature over time in Simulink. Which approach best uses Simulink's strength to model this dynamic system?

hard

A. Write a static equation and solve it once without feedback

B. Use blocks to represent temperature sensors, heaters, and feedback loops to simulate temperature changes

C. Use Simulink only to draw the system diagram without simulation

D. Model the system as a fixed constant value since temperature is stable

Solution

1. Step 1: Identify the nature of the heating system

   The heating system changes temperature over time, so it is a dynamic system requiring simulation of changing states.

2. Step 2: Choose the modeling approach

   Simulink uses blocks and feedback loops to represent parts and their interactions over time, which fits modeling sensors and heaters with feedback controlling temperature.

3. Final Answer:

   Use blocks to represent temperature sensors, heaters, and feedback loops to simulate temperature changes -> Option B

4. Quick Check:

   Dynamic system needs blocks and feedback [OK]

Hint: Model changing parts and feedback with blocks [OK]

Common Mistakes:

• Using static equations for dynamic behavior
• Ignoring feedback loops
• Thinking Simulink only draws diagrams