Interpolation (interp1) in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of interp1 with linear method

What is the output of the following MATLAB code snippet?

MATLAB

x = [1 2 3 4 5];
y = [10 20 30 40 50];
xi = 2.5;
yi = interp1(x, y, xi, 'linear');
disp(yi);

A 25

B 20

C 30

D Error: Undefined function or variable 'interp1'

💡 Hint

Linear interpolation finds the value halfway between y(2) and y(3).

The value at xi=2.5 is halfway between y(2)=20 and y(3)=30, so the output is 25.

❓ Predict Output

intermediate

Output of interp1 with 'nearest' method

What will be the output of this MATLAB code?

MATLAB

x = [0 1 2 3 4];
y = [0 10 20 30 40];
xi = 2.7;
yi = interp1(x, y, xi, 'nearest');
disp(yi);

A 30

B 27

C 20

D Error: Input data must be strictly increasing

💡 Hint

Nearest method picks the y value of the closest x point.

2.7 is closer to 3 than 2, so yi = y(4) = 30.

❓ Predict Output

advanced

interp1 with 'spline' method output

What is the output of this MATLAB code snippet?

MATLAB

x = [1 2 3 4];
y = [1 4 9 16];
xi = 2.5;
yi = interp1(x, y, xi, 'spline');
disp(round(yi,2));

A 8.50

B 7.25

C 6.56

D Error: Method 'spline' not supported

💡 Hint

Spline interpolation fits a smooth curve through points.

The spline interpolation at 2.5 gives approximately 6.56 after rounding.

❓ Predict Output

advanced

interp1 with extrapolation option

What is the output of this MATLAB code?

MATLAB

x = [1 2 3];
y = [2 4 6];
xi = 4;
yi = interp1(x, y, xi, 'linear', 'extrap');
disp(yi);

A 6

B 8

C NaN

D Error: Extrapolation not allowed

💡 Hint

Extrapolation extends the linear trend beyond known points.

Linear extrapolation beyond x=3 gives yi=8 at x=4.

🧠 Conceptual

expert

Error type from invalid interp1 input

What error does MATLAB produce when calling interp1 with non-monotonic x vector like this? x = [1 3 2 4]; y = [10 30 20 40]; xi = 2.5; interp1(x, y, xi);

A No error, returns interpolated value.

B Error using interp1: Y must be a vector of the same length as X.

C Error using interp1: XI must be within the range of X.

D Error using interp1: X must be strictly monotonic increasing or decreasing.

💡 Hint

interp1 requires x to be sorted strictly increasing or decreasing.

The x vector is not strictly monotonic, so interp1 throws an error about monotonicity.