Animation basics in MATLAB - Mini Project: Build & Apply

Animation basics

📖 Scenario: You want to create a simple animation in MATLAB that shows a point moving along a sine wave. This is useful for understanding how to update plots dynamically.

🎯 Goal: Build a MATLAB script that animates a point moving along the sine curve from 0 to 2π.

📋 What You'll Learn

Create a vector of x values from 0 to 2π

Create a vector of y values as sine of x

Set up a figure and plot the initial point

Update the point position in a loop to animate movement

Use pause to control animation speed

💡 Why This Matters

🌍 Real World

Animating data points helps visualize changes over time, useful in physics simulations, engineering, and data analysis.

💼 Career

Understanding animation basics in MATLAB is valuable for engineers and scientists who need to present dynamic data clearly.

1

Create the data vectors

Create a vector called x with 100 points linearly spaced between 0 and 2*pi. Then create a vector called y where each element is the sine of the corresponding x value.

MATLAB

% Your code here to create x and y vectors

Hint

Use linspace to create evenly spaced points and sin to get sine values.

2

Set up the figure and initial plot

Create a figure window and plot the first point of the sine wave using plot with a red circle marker. Store the plot handle in a variable called h.

MATLAB

x = linspace(0, 2*pi, 100);
y = sin(x);
% Your code here to create figure and plot initial point

Hint

Use plot to draw the point and axis to set the viewing window.

3

Animate the point along the sine wave

Use a for loop with variable i from 1 to 100. Inside the loop, update the XData and YData properties of h to the i-th elements of x and y. Use pause(0.05) to slow down the animation.

MATLAB

x = linspace(0, 2*pi, 100);
y = sin(x);
figure;
h = plot(x(1), y(1), 'ro', 'MarkerSize', 10, 'MarkerFaceColor', 'r');
axis([0 2*pi -1.5 1.5]);
grid on;
% Your code here to animate the point

Hint

Change the XData and YData of the plot handle inside the loop.

4

Display the animation result

Run the script to see the red point move smoothly along the sine wave from left to right.

MATLAB

x = linspace(0, 2*pi, 100);
y = sin(x);
figure;
h = plot(x(1), y(1), 'ro', 'MarkerSize', 10, 'MarkerFaceColor', 'r');
axis([0 2*pi -1.5 1.5]);
grid on;
for i = 1:100
    h.XData = x(i);
    h.YData = y(i);
    pause(0.05);
end
% Run the script to see the animation

Hint

Run the whole script in MATLAB. You should see a red dot moving along the sine curve.

Practice

1. What is the main purpose of using drawnow in a MATLAB animation loop?

easy

A. To update the figure window and show the latest plot changes immediately

B. To pause the animation for a fixed time

C. To clear the figure before plotting new data

D. To set the axis limits for the plot

Solution

1. Step 1: Understand the role of drawnow

   drawnow forces MATLAB to update the figure window immediately with any changes made to the plot.

2. Step 2: Differentiate from other commands

   Unlike pause which delays execution, drawnow just refreshes the display without stopping the code.

3. Final Answer:

   To update the figure window and show the latest plot changes immediately -> Option A

4. Quick Check:

   drawnow updates display immediately [OK]

Hint: Remember: drawnow refreshes the plot instantly [OK]

Common Mistakes:

• Confusing drawnow with pause
• Thinking drawnow clears the plot
• Using drawnow to set axis limits

2. Which of the following is the correct syntax to create a simple animation loop in MATLAB?

easy

A. loop i in 1:10 { plot(i, i^2); pause(0.5); drawnow; }

B. for i = 1 to 10; plot(i, i^2); pause(0.5); drawnow; end

C. for i = 1:10; plot(i, i^2); pause(0.5); drawnow; end

D. while i <= 10; plot(i, i^2); pause(0.5); drawnow; i++; end

Solution

1. Step 1: Check MATLAB loop syntax

   MATLAB uses for variable = range syntax, so for i = 1:10 is correct.

2. Step 2: Verify loop body and commands

   The commands plot, pause, and drawnow are correctly placed and separated by semicolons.

3. Final Answer:

   for i = 1:10; plot(i, i^2); pause(0.5); drawnow; end -> Option C

4. Quick Check:

   MATLAB for-loop uses '=' and ':' [OK]

Hint: MATLAB loops use 'for var = range' syntax [OK]

Common Mistakes:

• Using 'for i = 1 to 10' which is invalid
• Using curly braces {} for loops
• Using i++ which is not MATLAB syntax

3. What will be the visible effect of running this MATLAB code?

figure;
axis([0 10 0 100]);
for x = 1:10
    y = x^2;
    plot(x, y, 'ro');
    drawnow;
    pause(0.3);
end

medium

A. Only the last red dot at (10,100) is visible

B. All red dots appear at once after the loop finishes

C. The plot window stays blank with no dots

D. Red dots appear one by one at points (1,1), (2,4), ..., (10,100)

Solution

1. Step 1: Understand the loop plotting behavior

   Each iteration plots a red circle at (x, x^2) and calls drawnow to update the figure immediately.

2. Step 2: Effect of axis limits and pause

   Axis limits prevent resizing, and pause(0.3) delays so dots appear one by one.

3. Final Answer:

   Red dots appear one by one at points (1,1), (2,4), ..., (10,100) -> Option D

4. Quick Check:

   drawnow + pause shows points sequentially [OK]

Hint: drawnow + pause shows animation step-by-step [OK]

Common Mistakes:

• Thinking all points appear at once
• Assuming plot clears previous points
• Ignoring axis limits effect

4. Identify the error in this MATLAB animation code:

for t = 1:5
    plot(t, t^2, 'bo');
    pause(0.5);
end

medium

A. Missing drawnow to update the plot window

B. Incorrect plot marker symbol 'bo'

C. Loop variable t should start from 0

D. Pause duration is too short for animation

Solution

1. Step 1: Check for plot update command

   The code plots points but does not call drawnow, so the figure may not update during the loop.

2. Step 2: Understand effect of missing drawnow

   Without drawnow, MATLAB delays updating the figure until the loop ends, so animation won't show step-by-step.

3. Final Answer:

   Missing drawnow to update the plot window -> Option A

4. Quick Check:

   Always use drawnow to refresh animation frames [OK]

Hint: Use drawnow inside loops to refresh plots [OK]

Common Mistakes:

• Thinking pause alone updates the plot
• Changing loop start without reason
• Confusing marker symbols with errors

5. You want to animate a moving sine wave in MATLAB without flickering or resizing. Which approach is best?

hard

A. Clear figure inside loop, plot new sine wave, use pause only

B. Set fixed axis limits before the loop, update plot data inside loop, use drawnow and pause

C. Plot sine wave once outside loop, then update axis limits inside loop

D. Use pause inside loop without drawnow or axis limits

Solution

1. Step 1: Prevent flickering by fixing axis limits

   Setting axis limits before the loop stops MATLAB from resizing the plot each frame, avoiding flicker.

2. Step 2: Update plot data and refresh display properly

   Update the sine wave data inside the loop, then call drawnow to refresh and pause to control speed.

3. Final Answer:

   Set fixed axis limits before the loop, update plot data inside loop, use drawnow and pause -> Option B

4. Quick Check:

   Fixed axis + drawnow + pause = smooth animation [OK]

Hint: Fix axis limits before loop to avoid flicker [OK]

Common Mistakes:

• Clearing figure each loop causing flicker
• Not fixing axis limits causing resizing
• Using pause without drawnow