Multiple plots (hold on) in MATLAB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the hold on command do in MATLAB plotting?

It keeps the current plot active so that new plots are added to the same figure instead of replacing it.

beginner

How do you plot two different lines on the same figure in MATLAB?

Use plot for the first line, then hold on, then plot again for the second line.

beginner

What command stops adding plots to the current figure and allows new plots to replace it?

The command hold off stops adding to the current plot and resets to default behavior.

beginner

True or False: Without hold on, calling plot multiple times will overwrite the previous plot.

True. Each plot call replaces the existing plot unless hold on is used.

intermediate

What is the effect of hold on on axis limits and labels?

It preserves the current axis limits and labels so they are not reset when new plots are added.

What happens if you plot twice in MATLAB without using hold on?

A The figure window closes.

B Both plots appear on the same figure automatically.

C MATLAB shows an error.

D The second plot replaces the first plot.

Without hold on, each new plot command clears the previous plot.

Which command allows you to add multiple plots to the same figure in MATLAB?

A hold off

B hold on

C plot add

D figure hold

hold on keeps the current plot so new plots add to it.

After using hold on, how do you return to the default plotting behavior?

A hold off

B hold reset

C plot reset

D clear hold

hold off stops adding plots to the current figure.

If you want to plot a sine and cosine wave on the same graph, what is the correct sequence?

A plot sine; hold on; plot cosine

B hold on; plot sine; plot cosine

C plot sine; plot cosine

D plot sine; hold off; plot cosine

You plot the first line, then use hold on before plotting the second.

What does hold on preserve when adding new plots?

A Only labels

B Only axis limits

C Axis limits and labels

D Nothing is preserved

hold on keeps axis limits and labels unchanged when adding plots.

Explain how to plot multiple lines on the same figure in MATLAB using hold on.

Think about how to keep the figure active for new plots.

Describe what happens to the axis limits and labels when you use hold on in MATLAB.

Consider what would happen if the limits changed every time you add a plot.

Practice

1. What does the hold on command do in MATLAB plotting?

easy

A. Clears the current figure before plotting new data.

B. Allows multiple plots to be drawn on the same figure without erasing previous plots.

C. Saves the current plot to a file.

D. Changes the color of the plot lines automatically.

Solution

1. Step 1: Understand the purpose of hold on

   The hold on command tells MATLAB to keep the current plot and add new plots on top of it.

2. Step 2: Compare with other options

   Other commands like hold off or default plotting clear the figure before new plots, so they do not allow multiple plots together.

3. Final Answer:

   Allows multiple plots to be drawn on the same figure without erasing previous plots. -> Option B

4. Quick Check:

   hold on = multiple plots on one figure [OK]

Hint: Remember: hold on means keep adding plots [OK]

Common Mistakes:

• Thinking hold on clears the figure
• Confusing hold on with saving plots
• Assuming hold on changes plot colors

2. Which of the following is the correct way to plot two lines on the same figure in MATLAB?

easy

A. plot(x1, y1); hold on; plot(x2, y2); hold off;

B. hold on; plot(x1, y1); hold off; plot(x2, y2);

C. plot(x1, y1); plot(x2, y2);

D. plot(x1, y1); hold off; plot(x2, y2);

Solution

1. Step 1: Identify the correct sequence to keep multiple plots

   Using hold on after the first plot keeps it visible for the second plot.

2. Step 2: Confirm proper use of hold off

   Calling hold off after plotting both lines resets plotting behavior for future plots.

3. Final Answer:

   plot(x1, y1); hold on; plot(x2, y2); hold off; -> Option A

4. Quick Check:

   Use hold on between plots to combine them [OK]

Hint: Use hold on right after first plot to add more [OK]

Common Mistakes:

• Not using hold on before second plot
• Using hold off too early
• Plotting without hold on clears previous plot

3. What will be the output of the following MATLAB code?

t = 0:0.1:1;
plot(t, t);
hold on;
plot(t, t.^2);

medium

A. Two plots will appear: a straight line and a curve on the same figure.

B. Only the plot of t vs t^2 will be shown.

C. An error will occur because hold on is used incorrectly.

D. Only the plot of t vs t will be shown.

Solution

1. Step 1: Analyze the first plot command

   The first plot draws a straight line y = t on the figure.

2. Step 2: Understand the effect of hold on and second plot

   Using hold on keeps the first plot visible, so the second plot y = t^2 is drawn on the same figure as a curve.

3. Final Answer:

   Two plots will appear: a straight line and a curve on the same figure. -> Option A

4. Quick Check:

   hold on keeps previous plot, so both appear [OK]

Hint: hold on keeps old plots visible for new ones [OK]

Common Mistakes:

• Thinking only last plot shows
• Assuming hold on causes error
• Confusing plot commands order

4. Identify the error in this MATLAB code that tries to plot two lines on the same figure:

plot(x, y1)
hold off
plot(x, y2)

medium

A. There is no error; the code works correctly.

B. The variable x is not defined.

C. hold off should be called before the first plot.

D. hold off should be replaced with hold on to keep both plots visible.

Solution

1. Step 1: Understand the effect of hold off

   Calling hold off resets plotting to clear the figure before the next plot.

2. Step 2: Identify correct command to keep plots

   To keep both plots visible, hold on should be used instead of hold off.

3. Final Answer:

   hold off should be replaced with hold on to keep both plots visible. -> Option D

4. Quick Check:

   Use hold on to combine plots, not hold off [OK]

Hint: hold off clears plots; use hold on to keep them [OK]

Common Mistakes:

• Using hold off instead of hold on
• Thinking hold off adds plots
• Ignoring hold commands altogether

5. You want to plot three different data sets on the same figure with different colors and then reset plotting to default for future plots. Which sequence of commands is correct?

hard

A. plot(x1, y1, 'r'); plot(x2, y2, 'g'); plot(x3, y3, 'b'); hold on; hold off;

B. hold on; plot(x1, y1, 'r'); plot(x2, y2, 'g'); plot(x3, y3, 'b');

C. plot(x1, y1, 'r'); hold on; plot(x2, y2, 'g'); plot(x3, y3, 'b'); hold off;

D. plot(x1, y1, 'r'); hold off; plot(x2, y2, 'g'); hold on; plot(x3, y3, 'b');

Solution

1. Step 1: Use hold on after first plot to combine multiple plots

   After plotting the first data set, hold on keeps the figure active for additional plots.

2. Step 2: Plot all data sets with specified colors and then reset with hold off

   Plotting the second and third data sets adds them to the same figure. Calling hold off resets plotting behavior for future plots.

3. Final Answer:

   plot(x1, y1, 'r'); hold on; plot(x2, y2, 'g'); plot(x3, y3, 'b'); hold off; -> Option C

4. Quick Check:

   hold on after first plot, hold off after last plot [OK]

Hint: hold on after first plot, hold off after last [OK]

Common Mistakes:

• Not calling hold off after multiple plots
• Calling hold on before first plot
• Mixing hold on and hold off incorrectly