Labels, title, and legend in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this MATLAB plot labeling code?

Consider the following MATLAB code that plots a simple line and adds labels and a title. What text will appear as the x-axis label?

MATLAB

x = 1:5;
y = x.^2;
plot(x, y);
xlabel('Time (s)');
ylabel('Distance (m)');
title('Distance vs Time');

A Time (s)

B Distance (m)

C Distance vs Time

D x-axis

💡 Hint

Look for the function that sets the label for the x-axis.

The function xlabel('Time (s)') sets the label for the x-axis to 'Time (s)'.

❓ Predict Output

intermediate

What legend text appears in this MATLAB plot?

Given this MATLAB code, what text will appear in the legend?

MATLAB

x = 0:0.1:2*pi;
y1 = sin(x);
y2 = cos(x);
plot(x, y1, '-r', x, y2, '-b');
legend('Sine Wave', 'Cosine Wave');

A sin and cos

B Sine Wave and Cosine Wave

C Red and Blue lines

D Sine and Cosine

💡 Hint

Check the legend function arguments.

The legend function is called with 'Sine Wave' and 'Cosine Wave', so these exact texts appear in the legend.

🔧 Debug

advanced

Why does this MATLAB code not display the title?

This MATLAB code plots data and tries to add a title, but the title does not appear. What is the problem?

MATLAB

x = 1:10;
y = rand(1,10);
plot(x,y)
title = 'Random Data Plot';

A The plot command is missing a semicolon

B The x and y vectors have different lengths

C The y data is not sorted

D The title is assigned to a variable instead of calling the title() function

💡 Hint

Check how the title is set in MATLAB.

The code assigns a string to a variable named title instead of calling the title() function, so no title is displayed.

🧠 Conceptual

advanced

What happens if you call legend without arguments after plotting multiple lines?

In MATLAB, after plotting multiple lines, what does calling legend() with no arguments do?

A It automatically creates a legend using the DisplayName properties of plotted lines

B It clears any existing legend from the plot

C It creates an empty legend box

D It causes a syntax error

💡 Hint

Think about how MATLAB uses DisplayName properties in plots.

Calling legend() without arguments uses the DisplayName properties of plotted lines to create a legend automatically.

❓ Predict Output

expert

What is the output of this MATLAB code with multiple labels and legend?

Analyze this MATLAB code and determine what text appears as the y-axis label and what the legend shows.

MATLAB

x = linspace(0,1,5);
y1 = x;
y2 = x.^2;
plot(x,y1,'-o', x,y2,'-s');
ylabel('Value');
legend({'Linear','Quadratic'});
title('Comparison Plot');

A y-axis label: 'Comparison Plot'; legend: 'Linear' and 'Quadratic'

B y-axis label: 'Value'; legend: 'y1' and 'y2'

C y-axis label: 'Value'; legend: 'Linear' and 'Quadratic'

D y-axis label: 'Value'; legend: 'o' and 's'

💡 Hint

Check the ylabel and legend function arguments carefully.

ylabel('Value') sets the y-axis label to 'Value'. legend({'Linear','Quadratic'}) sets the legend text accordingly.

Practice

1. Which MATLAB function is used to add a label to the x-axis of a plot?

easy

A. xlabel

B. ylabel

C. title

D. legend

Solution

1. Step 1: Understand axis labeling functions

   In MATLAB, xlabel labels the x-axis, ylabel labels the y-axis, title adds a main heading, and legend explains plot lines.

2. Step 2: Identify the function for x-axis label

   The function xlabel is specifically designed to add a label to the x-axis.

3. Final Answer:

   xlabel -> Option A

4. Quick Check:

   Label x-axis = xlabel [OK]

Hint: Use xlabel for x-axis label, ylabel for y-axis [OK]

Common Mistakes:

• Confusing xlabel with ylabel
• Using title instead of axis labels
• Using legend for axis labels

2. Which of the following is the correct syntax to add a legend to a plot with two lines labeled 'Data1' and 'Data2'?

easy

A. legend{'Data1', 'Data2'}

B. legend = ('Data1', 'Data2')

C. legend['Data1', 'Data2']

D. legend('Data1', 'Data2')

Solution

1. Step 1: Recall correct legend syntax

   In MATLAB, the function legend is called with parentheses and string arguments to label plot lines.

2. Step 2: Identify correct syntax

   The correct syntax uses parentheses and comma-separated strings: legend('Data1', 'Data2'). Other options use invalid assignment or brackets.

3. Final Answer:

   legend('Data1', 'Data2') -> Option D

4. Quick Check:

   legend('labels') uses parentheses [OK]

Hint: Use legend('label1', 'label2') with parentheses [OK]

Common Mistakes:

• Using assignment '=' instead of function call
• Using square or curly brackets
• Missing quotes around labels

3. What will be the title of the plot after running this MATLAB code?

plot(1:5, [2 4 6 8 10]);
title('Sales Over Time');

medium

A. plot(1:5, [2 4 6 8 10])

B. Sales Over Time

C. 1:5

D. No title

Solution

1. Step 1: Understand the title function

   The title function sets the main heading of the plot to the given string.

2. Step 2: Check the given code

   The code calls title('Sales Over Time'), so the plot's title will be exactly 'Sales Over Time'.

3. Final Answer:

   Sales Over Time -> Option B

4. Quick Check:

   title('text') sets plot title [OK]

Hint: title('text') sets the plot's main heading [OK]

Common Mistakes:

• Confusing title with axis labels
• Expecting variable values as title
• No title if title function missing

4. Identify the error in this MATLAB code snippet:

plot(x, y);
xlabel = 'Time';
ylabel('Value');
legend('Line1');

medium

A. Using assignment '=' with xlabel instead of function call

B. Missing ylabel function call

C. legend syntax is incorrect

D. plot function is missing arguments

Solution

1. Step 1: Check xlabel usage

   The code uses xlabel = 'Time'; which assigns a string to variable xlabel instead of calling the function xlabel('Time').

2. Step 2: Verify other lines

   ylabel('Value') and legend('Line1') are correctly called as functions. The plot function has arguments x, y assumed defined.

3. Final Answer:

   Using assignment '=' with xlabel instead of function call -> Option A

4. Quick Check:

   Use xlabel('text'), not xlabel = 'text' [OK]

Hint: Call xlabel as function: xlabel('text'), not assignment [OK]

Common Mistakes:

• Assigning xlabel instead of calling function
• Confusing ylabel syntax
• Incorrect legend usage

5. You have plotted two data sets on the same graph using:

plot(x, y1, '-r', x, y2, '-b');

How do you add a title 'Comparison', label the x-axis as 'Time', the y-axis as 'Value', and add a legend with labels 'Data1' and 'Data2'?

hard

A. title = 'Comparison'; xlabel = 'Time'; ylabel = 'Value'; legend = ('Data1', 'Data2');

B. title('Comparison'); xlabel('Time'); ylabel('Value'); legend(['Data1', 'Data2']);

C. title('Comparison'); xlabel('Time'); ylabel('Value'); legend('Data1', 'Data2');

D. title('Comparison'); xlabel('Time'); ylabel('Value'); legend{'Data1', 'Data2'};

Solution

1. Step 1: Use correct function calls for labels and title

   Functions title, xlabel, and ylabel require parentheses with string arguments.

2. Step 2: Use correct legend syntax

   The legend function takes comma-separated strings inside parentheses, not assignment or brackets.

3. Final Answer:

   title('Comparison'); xlabel('Time'); ylabel('Value'); legend('Data1', 'Data2'); -> Option C

4. Quick Check:

   Use function calls with parentheses for labels and legend [OK]

Hint: Use function calls with parentheses for all labels and legend [OK]

Common Mistakes:

• Assigning strings instead of calling functions
• Using brackets or braces for legend
• Missing quotes around labels