Animation basics in MATLAB - Step-by-Step Execution

Concept Flow - Animation basics

Initialize figure and plot

↓

Start loop over frames

↓

Update plot data

↓

Refresh display with drawnow

↓

Pause for animation speed

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Check if more frames

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Repeat

The animation starts by setting up a plot, then repeatedly updates the plot data inside a loop, refreshing the display each time until all frames are shown.

Execution Sample

MATLAB

x = linspace(0,2*pi,100);
fig = figure;
h = plot(x,sin(x));
for k = 1:50
    y = sin(x + k*0.1);
    set(h, 'YData', y);
    drawnow;
    pause(0.05);
end

This code animates a sine wave moving to the right by updating the plot's Y data in a loop.

Execution Table

Step	k (frame)	y (sin values)	Action	Display Update
1	1	sin(x + 0.1)	Set YData to y	Plot shows sine wave shifted by 0.1
2	2	sin(x + 0.2)	Set YData to y	Plot updates to sine wave shifted by 0.2
3	3	sin(x + 0.3)	Set YData to y	Plot updates to sine wave shifted by 0.3
...	...	...	...	...
50	50	sin(x + 5.0)	Set YData to y	Plot updates to sine wave shifted by 5.0
51	End	N/A	Loop ends	Animation stops

💡 Loop ends after 50 frames, animation complete

Variable Tracker

Variable	Start	After 1	After 2	After 3	...	After 50	Final
k	N/A	1	2	3	...	50	End
y	sin(x + 0)	sin(x + 0.1)	sin(x + 0.2)	sin(x + 0.3)	...	sin(x + 5.0)	N/A

Key Moments - 3 Insights

Why do we use 'set(h, 'YData', y)' instead of re-plotting inside the loop?

Using 'set' updates the existing plot efficiently without creating a new plot each time, as shown in the execution_table rows where only YData changes but the plot handle 'h' stays the same.

What is the role of 'drawnow' in the animation loop?

'drawnow' forces MATLAB to refresh the figure window immediately after updating YData, so the animation appears smooth, as seen in each step's Display Update.

Why do we include 'pause(0.05)' in the loop?

'pause' slows down the loop so the animation is visible to our eyes, otherwise it would run too fast to see changes, matching the timing between steps in the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table at step 3, what is the value of k and what action is performed?

A k=3, re-plot entire graph

B k=2, set YData to sin(x + 0.2)

C k=3, set YData to sin(x + 0.3)

D k=1, set YData to sin(x + 0.1)

💡 Hint

Check row 3 in execution_table for k and Action columns

At which step does the animation loop end according to the execution_table?

A Step 50

B Step 51

C Step 1

D Step 100

💡 Hint

Look at the exit_note and last row in execution_table

If we remove 'pause(0.05)', what would happen to the animation speed?

A Animation would run faster and might appear jumpy

B Animation would run slower

C Animation would stop

D No change in animation speed

💡 Hint

Refer to key_moments explanation about 'pause' slowing the loop

Concept Snapshot

Animation basics in MATLAB:
- Initialize figure and plot once
- Use a loop to update plot data (e.g., YData)
- Use 'set' to update plot efficiently
- Call 'drawnow' to refresh display
- Use 'pause' to control animation speed
- Loop ends after desired frames

Full Transcript

This animation example in MATLAB starts by creating a figure and plotting a sine wave. Then, inside a loop from 1 to 50, it updates the sine wave by shifting it horizontally. The plot's YData is updated using 'set', and 'drawnow' refreshes the figure so the change is visible. A short pause slows the loop so the animation can be seen clearly. The loop ends after 50 frames, completing the animation.