Scope and display blocks in MATLAB - Step-by-Step Execution

Concept Flow - Scope and display blocks

Start MATLAB Script

↓

Define Variables

↓

Use Scope Block

↓

Use Display Block

↓

Run Simulation

↓

View Output in Scope

↓

View Output in Display

↓

End

This flow shows how MATLAB script defines variables, uses Scope and Display blocks, runs simulation, and views outputs.

Execution Sample

MATLAB

t = 0:0.1:1;
x = sin(2*pi*t);
disp(x(1));
plot(t,x);

This code creates a time vector, computes sine values, displays the first value, and plots the sine wave.

Execution Table

Step	Action	Variable/Block	Value/Output
1	Define time vector t	t	[0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0]
2	Calculate sine values x	x	[0 0.5878 0.9511 0.9511 0.5878 0 -0.5878 -0.9511 -0.9511 -0.5878 0]
3	Display first element of x	display block	0
4	Plot x vs t	scope block	Graph of sine wave shown
5	End of script	-	-

💡 Script ends after plotting and displaying values.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
t	undefined	[0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0]	[0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0]	[0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0]
x	undefined	undefined	[0 0.5878 0.9511 0.9511 0.5878 0 -0.5878 -0.9511 -0.9511 -0.5878 0]	[0 0.5878 0.9511 0.9511 0.5878 0 -0.5878 -0.9511 -0.9511 -0.5878 0]

Key Moments - 2 Insights

Why does the display block show only one number while the scope shows a graph?

The display block outputs a single value (x(1)) at one time, while the scope block plots the entire vector x against t, showing a continuous graph (see execution_table steps 3 and 4).

What happens if the variable is not defined before using the scope or display block?

MATLAB will give an error because the variable does not exist yet. Variables must be defined before being used in scope or display blocks (see variable_tracker start values).

Visual Quiz - 3 Questions

Look at the execution table, what is the value displayed by the display block at step 3?

A 0.5878

B 0

C 1

D Undefined

💡 Hint

Check the 'Value/Output' column at step 3 in the execution_table.

At which step is the sine wave plotted on the scope block?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look for the action mentioning plotting or scope block in the execution_table.

If the time vector t was changed to 0:0.2:1, how would the variable x change?

A x would have fewer elements corresponding to the new t

B x would remain the same length

C x would become longer

D x would be empty

💡 Hint

Refer to variable_tracker and how x depends on t length.

Concept Snapshot

Scope and Display blocks in MATLAB:
- Scope block shows signals as graphs over time.
- Display block shows numeric values in command window.
- Define variables before using blocks.
- Use scope for continuous signals, display for single values.
- Run simulation to see outputs.

Full Transcript

This visual execution trace shows how MATLAB uses scope and display blocks. First, a time vector t is created from 0 to 1 in steps of 0.1. Then, x is calculated as the sine of 2*pi*t. The display block outputs the first value of x, which is 0. The scope block plots the entire sine wave x against time t. Variables t and x are tracked step by step. Key moments clarify why display shows one value and scope shows a graph, and the importance of defining variables before use. The quiz tests understanding of output values, plotting steps, and how changing t affects x.

Practice

1. What is the main purpose of a Scope block in Simulink?

easy

A. To show numeric values in the workspace

B. To display signal graphs during simulation

C. To save simulation data to a file

D. To generate code from the model

Solution

1. Step 1: Understand the function of Scope blocks

   Scope blocks are used to visualize signals as graphs during simulation.

2. Step 2: Compare with other options

   Other options describe different functionalities not related to Scope blocks.

3. Final Answer:

   To display signal graphs during simulation -> Option B

4. Quick Check:

   Scope = signal graphs [OK]

Hint: Scope shows graphs, Display shows numbers [OK]

Common Mistakes:

• Confusing Scope with Display block
• Thinking Scope saves data
• Assuming Scope shows numeric values

2. Which of the following is the correct way to add a Display block in Simulink?

easy

A. Drag the Display block from the Simulink library to the model

B. Write display() in the MATLAB command window

C. Use the Scope block and rename it to Display

D. Add a To Workspace block and rename it Display

Solution

1. Step 1: Identify how to add blocks in Simulink

   Blocks are added by dragging them from the Simulink library browser into the model.

2. Step 2: Check other options

   Options A, B, and D describe incorrect or unrelated methods.

3. Final Answer:

   Drag the Display block from the Simulink library to the model -> Option A

4. Quick Check:

   Add blocks by dragging from library [OK]

Hint: Add blocks by dragging from library browser [OK]

Common Mistakes:

• Trying to add blocks via MATLAB commands
• Renaming blocks instead of adding correct ones
• Confusing Display with To Workspace block

3. Consider this Simulink model snippet: a sine wave connected to both a Scope and a Display block. What will you see during simulation?

medium

A. Both Scope and Display show numeric values

B. The Scope shows numeric values; the Display shows a graph

C. The Scope shows a graph of the sine wave; the Display shows the current numeric value

D. Neither block shows any output

Solution

1. Step 1: Understand Scope and Display outputs

   Scope shows signal graphs; Display shows current numeric values during simulation.

2. Step 2: Apply to sine wave input

   The sine wave signal will appear as a graph on Scope and as changing numbers on Display.

3. Final Answer:

   The Scope shows a graph of the sine wave; the Display shows the current numeric value -> Option C

4. Quick Check:

   Scope = graph, Display = number [OK]

Hint: Scope graphs signals; Display shows live numbers [OK]

Common Mistakes:

• Mixing up graph and numeric display
• Expecting Display to show full signal history
• Thinking Scope shows only numbers

4. You added a Scope block but it shows no signal during simulation. What is the most likely cause?

medium

A. The model has no input blocks

B. The Display block is missing

C. The simulation is paused

D. The Scope block is not connected to any signal

Solution

1. Step 1: Check Scope connection

   Scope must be connected to a signal line to display data.

2. Step 2: Consider other options

   Display block absence does not affect Scope; simulation paused would freeze output; no input blocks means no signals.

3. Final Answer:

   The Scope block is not connected to any signal -> Option D

4. Quick Check:

   Scope needs signal connection [OK]

Hint: Scope must connect to signal to show output [OK]

Common Mistakes:

• Assuming Display block affects Scope output
• Not checking signal connections
• Ignoring simulation state

5. You want to monitor multiple signals simultaneously during simulation and see both their graphs and numeric values updated live. Which combination of blocks should you use?

hard

A. Multiple Scope blocks and multiple Display blocks, each connected to one signal

B. One Scope block connected to all signals and one Display block connected to all signals

C. One Display block connected to all signals only

D. Multiple Display blocks connected to one signal each, no Scope blocks

Solution

1. Step 1: Understand monitoring multiple signals

   Each Scope or Display block connects to one signal to show its graph or numeric value.

2. Step 2: Evaluate options

   One Scope or Display cannot connect to multiple signals directly; multiple blocks are needed.

3. Final Answer:

   Multiple Scope blocks and multiple Display blocks, each connected to one signal -> Option A

4. Quick Check:

   One block per signal for graph and number [OK]

Hint: Use one block per signal to monitor multiple signals [OK]

Common Mistakes:

• Trying to connect one block to many signals
• Ignoring need for multiple displays
• Confusing Scope and Display capabilities