MAT file save and load in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after saving and loading variables?

Consider the following MATLAB code that saves variables to a MAT file and then loads them back. What will be the value of result after running all commands?

MATLAB

a = 5;
b = 10;
save('data.mat', 'a', 'b');
clear a b
load('data.mat');
result = a + b;

A Error: Undefined variable 'a'.

B 0

C 15

D 5

💡 Hint

Remember that save stores variables to a file and load restores them into the workspace.

The variables a and b are saved to 'data.mat'. After clearing them, load brings them back. So, result = a + b = 5 + 10 = 15.

❓ Predict Output

intermediate

What happens when loading a MAT file with a missing variable?

Given the following MATLAB commands, what will be the output of whos after loading?

MATLAB

x = 42;
save('file.mat', 'x');
clear x
load('file.mat', 'y');
vars = whos;

A Error: Variable 'y' not found in file.mat

B vars is empty (no variables loaded)

C vars contains variable 'y' with value 42

D vars contains variable 'x' with value 42

💡 Hint

Loading a variable name that does not exist in the MAT file does not load anything.

The MAT file contains only variable 'x'. Loading 'y' which does not exist results in no variables loaded. So vars is empty.

🔧 Debug

advanced

Why does this MAT file load fail with an error?

Examine the code below. It tries to save and load a variable but causes an error on load. What is the cause?

MATLAB

data = rand(3);
save('mydata.mat', 'data');
clear data
load('mydata.mat', 'Data');

A No error, variable 'Data' is loaded correctly

B Error because file 'mydata.mat' does not exist

C Error because 'clear data' removes the file

D Error because variable name 'Data' does not match saved variable 'data' (case sensitive)

💡 Hint

MATLAB variable names are case sensitive when loading specific variables.

The saved variable is named 'data' (lowercase). Loading 'Data' (uppercase D) fails because it does not exist in the file.

📝 Syntax

advanced

Which option correctly saves multiple variables to a MAT file?

Select the correct MATLAB command to save variables a, b, and c into a file named 'vars.mat'.

A save('vars.mat', 'a', 'b', 'c');

B save('vars.mat', a, b, c);

C save('vars.mat', [a b c]);

D save('vars.mat', {'a', 'b', 'c'});

💡 Hint

Variable names must be passed as strings to the save function.

The save function requires variable names as strings to save them. Option A correctly passes the names as strings.

🚀 Application

expert

How many variables are loaded from this MAT file?

Suppose a MAT file 'mixed.mat' contains variables x, y, and z. What is the number of variables in the workspace after running this code?

MATLAB

load('mixed.mat', 'x', 'z');
vars = whos;

A 2

B 1

C 3

D 0

💡 Hint

Only variables specified in the load command are loaded.

Only variables 'x' and 'z' are loaded, so vars contains 2 variables.