Building block diagrams in MATLAB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a transfer function with numerator 1 and denominator [1 1].

MATLAB

sys = tf([1], [1 1]);

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

A[1 1]

B[1 0]

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using a vector for numerator instead of scalar

Confusing numerator and denominator

The numerator of the transfer function should be 1, so the correct input is 1.

2fill in blank

medium

Complete the code to connect two transfer functions in series.

MATLAB

sys_series = series(sys1, [1]);

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

Atf1

Bsys1

Csys2

Dsys

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same system twice

Using undefined variable names

To connect two systems in series, use the second system variable, here sys2.

3fill in blank

hard

Fix the error in the code to create a feedback connection with unity feedback.

MATLAB

sys_feedback = feedback(sys, [1]);

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

A1

Btf(1)

C0

Dsys

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same system as feedback

Using zero instead of one

Unity feedback means the feedback path is 1, so the correct input is 1.

4fill in blank

hard

Fill both blanks to create a closed-loop system with negative feedback.

MATLAB

closed_loop = feedback([1], [2]);

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

Asys

B1

C0

Dtf(1)

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping forward and feedback systems

Using zero feedback

The first blank is the forward system sys, and the second blank is the feedback system 1 for unity feedback.

5fill in blank

hard

Fill all three blanks to create a parallel connection of two systems and then feedback with unity.

MATLAB

parallel_sys = parallel([1], [2]);
closed_loop = feedback(parallel_sys, [3]);

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

Asys1

Bsys2

C1

Dsys

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same system twice in parallel

Incorrect feedback argument

The parallel connection uses sys1 and sys2, and the feedback is unity 1.

Practice

1. What is the primary purpose of building block diagrams in MATLAB Simulink?

easy

A. To write MATLAB scripts faster

B. To create 3D plots of data

C. To visually represent and simulate system behavior

D. To debug MATLAB code line by line

Solution

1. Step 1: Understand the role of block diagrams

   Block diagrams in Simulink are used to visually model systems by connecting blocks that represent components.

2. Step 2: Identify the main use

   They help simulate and analyze system behavior, not for scripting or plotting.

3. Final Answer:

   To visually represent and simulate system behavior -> Option C

4. Quick Check:

   Block diagrams = Visual system simulation [OK]

Hint: Block diagrams show system flow visually, not code or plots [OK]

Common Mistakes:

• Confusing block diagrams with MATLAB code scripts
• Thinking block diagrams create plots
• Assuming block diagrams debug code

2. Which of the following is the correct way to add a Gain block in a Simulink model using MATLAB command line?

easy

A. add_block('simulink/Math Operations/Gain', 'model/Gain1')

B. add_block('simulink/Sinks/Gain', 'model/Gain1')

C. add_block('simulink/Sources/Gain', 'model/Gain1')

D. add_block('simulink/Commonly Used Blocks/Gain', 'model/Gain1')

Solution

1. Step 1: Identify the correct library path for Gain block

   The Gain block is located under 'simulink/Math Operations' in Simulink library.

2. Step 2: Match the command syntax

   The command add_block('simulink/Math Operations/Gain', 'model/Gain1') correctly adds the Gain block to the model.

3. Final Answer:

   add_block('simulink/Math Operations/Gain', 'model/Gain1') -> Option A

4. Quick Check:

   Gain block path = Math Operations [OK]

Hint: Gain block is under Math Operations library [OK]

Common Mistakes:

• Using wrong library path for Gain block
• Confusing Sources or Sinks with Gain block location
• Incorrect syntax in add_block command

3. Consider this MATLAB code snippet for a Simulink model:

open_system('myModel');
add_block('simulink/Sources/Step', 'myModel/Step1');
add_block('simulink/Sinks/Scope', 'myModel/Scope1');
add_line('myModel', 'Step1/1', 'Scope1/1');

What will this code do?

medium

A. Create a model with a Step input but no connections

B. Create a model with a Step input connected to a Scope block

C. Create a model with a Gain block connected to a Scope block

D. Produce an error because add_line syntax is incorrect

Solution

1. Step 1: Analyze blocks added

   The code adds a Step block (input) and a Scope block (output) to the model 'myModel'.

2. Step 2: Analyze connection

   The add_line command connects output port 1 of Step1 to input port 1 of Scope1, linking input to output.

3. Final Answer:

   Create a model with a Step input connected to a Scope block -> Option B

4. Quick Check:

   Step block connected to Scope = Model created [OK]

Hint: add_line connects blocks by port numbers correctly [OK]

Common Mistakes:

• Confusing block types added
• Assuming no connection was made
• Thinking add_line syntax is wrong

4. You try to connect two blocks in Simulink using:

add_line('model', 'BlockA/1', 'BlockB/2');

but get an error. What is the most likely cause?

medium

A. add_line requires port numbers as strings, not numbers

B. BlockA does not have an output port 1

C. The model name is incorrect

D. BlockB does not have a second input port

Solution

1. Step 1: Understand port numbering

   Port numbers must exist on blocks; if BlockB/2 does not exist, connection fails.

2. Step 2: Check common error

   Most blocks have input port 1, but not all have a second input port, causing error.

3. Final Answer:

   BlockB does not have a second input port -> Option D

4. Quick Check:

   Invalid port number causes add_line error [OK]

Hint: Check if destination port exists before connecting [OK]

Common Mistakes:

• Assuming port numbers can be any number
• Thinking add_line syntax requires strings for ports
• Ignoring model name correctness

5. You want to create a Simulink model programmatically that sums two signals and then multiplies the result by 5. Which sequence of commands correctly builds this model?

hard

A. add_block('simulink/Math Operations/Sum', 'model/Sum1');
add_block('simulink/Math Operations/Gain', 'model/Gain1');
set_param('model/Gain1', 'Gain', '5');
add_line('model', 'Sum1/1', 'Gain1/1');

B. add_block('simulink/Math Operations/Gain', 'model/Gain1');
set_param('model/Gain1', 'Gain', '5');
add_block('simulink/Math Operations/Sum', 'model/Sum1');
add_line('model', 'Gain1/1', 'Sum1/1');

C. add_block('simulink/Math Operations/Sum', 'model/Sum1');
add_block('simulink/Math Operations/Gain', 'model/Gain1');
set_param('model/Gain1', 'Gain', '5');
add_line('model', 'Gain1/1', 'Sum1/1');

D. add_block('simulink/Math Operations/Sum', 'model/Sum1');
add_block('simulink/Math Operations/Gain', 'model/Gain1');
set_param('model/Gain1', 'Gain', '5');
add_line('model', 'Sum1/1', 'Gain1/2');

Solution

1. Step 1: Add Sum and Gain blocks correctly

   Sum block adds two inputs; Gain block multiplies by 5. Both blocks are added properly.

2. Step 2: Set Gain parameter and connect Sum output to Gain input

   Gain is set to 5. The output port 1 of Sum connects to input port 1 of Gain.

3. Final Answer:

   Correct sequence with Sum output connected to Gain input and Gain set to 5 -> Option A

4. Quick Check:

   Sum -> Gain with Gain=5 is correct [OK]

Hint: Connect Sum output to Gain input; set Gain parameter after adding block [OK]

Common Mistakes:

• Connecting Gain output to Sum input (wrong direction)
• Using wrong port numbers for connections
• Not setting Gain parameter correctly