plot3 for 3D lines in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple 3D line plot

What will be the output of the following MATLAB code snippet?

MATLAB

x = 1:5;
y = x.^2;
z = x + 1;
plot3(x, y, z, '-o');

A A 2D plot showing y vs x with circles

B Syntax error due to missing semicolon

C A 3D scatter plot without lines

D A 3D line plot with points marked by circles connecting (1,1,2) to (5,25,6)

💡 Hint

Remember plot3 plots lines in 3D space using x, y, and z coordinates.

The plot3 function connects points in 3D space with lines and markers. Here, x, y, and z are vectors of equal length, so it plots a 3D line with circle markers at each point.

🧠 Conceptual

intermediate

Understanding plot3 input vectors

Which of the following statements about the inputs to plot3(x,y,z) is TRUE?

A x, y, and z must be vectors of the same length to plot a 3D line.

B x, y, and z can be scalars or vectors of different lengths.

C Only x and y need to be vectors; z can be a scalar.

D plot3 only accepts matrices as inputs.

💡 Hint

Think about how points in 3D space are defined for a line.

plot3 connects points defined by corresponding elements in x, y, and z vectors. They must be the same length to form valid points.

🔧 Debug

advanced

Identify the error in 3D line plotting code

What error will the following MATLAB code produce?

MATLAB

x = 1:4;
y = [2 4 6];
z = 1:4;
plot3(x, y, z);

A Error: Vectors x, y, and z must be the same length.

B No error; plots a 3D line with missing points.

C Error: plot3 requires matrices, not vectors.

D Warning: y vector is shorter, MATLAB pads with zeros.

💡 Hint

Check the length of each vector used in plot3.

The y vector has length 3, while x and z have length 4. plot3 requires all input vectors to be the same length.

📝 Syntax

advanced

Correct syntax for plotting multiple 3D lines

Which option correctly plots two separate 3D lines in one figure?

MATLAB

x1 = 1:3; y1 = [2 3 4]; z1 = [1 0 1];
x2 = 3:5; y2 = [5 6 7]; z2 = [2 2 2];

A plot3(x1, y1); plot3(x2, y2, z2);

B plot3(x1, y1, z1); hold on; plot3(x2, y2, z2); hold off;

C plot3(x1, y1, z1, x2, y2, z2);

D plot3([x1 x2], [y1 y2], [z1 z2]);

💡 Hint

Use hold on to plot multiple lines in the same figure.

Option B plots the first line, then holds the plot to add the second line. Option B merges points into one line. Option B misses z for first line. Option B is invalid syntax.

🚀 Application

expert

Number of line segments in a 3D plot

Given vectors x, y, z each of length 10, how many line segments does plot3(x, y, z) draw?

A 11

B 10

C 9

D 8

💡 Hint

Each line segment connects two consecutive points.

With 10 points, plot3 connects point 1 to 2, 2 to 3, ..., 9 to 10, making 9 segments.