MAT file save and load in MATLAB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to save variable x to a MAT file named 'data.mat'.

MATLAB

x = 10;
save('[1]', 'x');

Drag options to blanks, or click blank then click option'

Adata.mat

Bfile.txt

Coutput.csv

Dimage.png

Attempts:

3 left

💡 Hint

Common Mistakes

Using a filename without .mat extension

Saving to a text or image file instead of MAT file

The save function saves variables to a MAT file. The filename must end with .mat.

2fill in blank

medium

Complete the code to load the variable x from the MAT file 'data.mat'.

MATLAB

load('[1]', 'x');

Drag options to blanks, or click blank then click option'

Afile.txt

Bdata.mat

Cimage.png

Doutput.csv

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to load from a non-MAT file

Using a wrong filename

The load function loads variables from a MAT file. You must specify the correct MAT filename.

3fill in blank

hard

Fix the error in the code to save variables a and b to 'myfile.mat'.

MATLAB

a = 5;
b = 7;
save('myfile.mat', [1]);

Drag options to blanks, or click blank then click option'

A'a', 'b'

B'a b'

C'a, b'

D'a',b

Attempts:

3 left

💡 Hint

Common Mistakes

Putting variable names in one string separated by commas or spaces

Missing quotes around variable names

To save multiple variables, list them as separate strings in the save function.

4fill in blank

hard

Fill both blanks to save variable y and load it back from 'file.mat'.

MATLAB

y = [1, 2, 3];
save('[1]', 'y');
clear y
load('[2]', 'y');

Drag options to blanks, or click blank then click option'

Afile.mat

Bdata.mat

Cmydata.mat

Doutput.mat

Attempts:

3 left

💡 Hint

Common Mistakes

Using different filenames for save and load

Forgetting to clear the variable before loading

Use the same filename to save and load the variable y.

5fill in blank

hard

Fill all three blanks to save variable z, clear it, and then load it back from 'test.mat'.

MATLAB

z = magic(3);
save('[1]', '[2]');
clear [3];
load('test.mat', 'z');

Drag options to blanks, or click blank then click option'

Atest.mat

Bz

Da

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong filename in save

Not clearing the correct variable

Saving variable name without quotes

Save to 'test.mat', save variable 'z', clear variable 'z' before loading it back.

Practice

1. What does the MATLAB command save('data.mat', 'x') do?

easy

A. Saves the variable x to a file named data.mat.

B. Loads the variable x from the file data.mat.

C. Deletes the variable x from the workspace.

D. Creates a new variable x with the name data.mat.

Solution

1. Step 1: Understand the save command

   The save command stores variables from the workspace into a MAT file.

2. Step 2: Analyze the given command

   save('data.mat', 'x') saves the variable x into the file named data.mat.

3. Final Answer:

   Saves the variable x to a file named data.mat. -> Option A

4. Quick Check:

   save stores variables [OK]

Hint: Remember: save stores, load retrieves variables [OK]

Common Mistakes:

• Confusing save with load command
• Thinking save deletes variables
• Assuming save creates variables

2. Which of the following is the correct syntax to load variables from a MAT file named results.mat?

easy

A. load('results.mat'); save;

B. load results.mat;

C. load = 'results.mat';

D. load('results.mat');

Solution

1. Step 1: Recall the syntax for loading MAT files

   The correct syntax to load variables from a MAT file is load('filename.mat').

2. Step 2: Check each option

   load('results.mat'); uses parentheses and quotes correctly: load('results.mat');. load results.mat; misses quotes, which causes an error. load = 'results.mat'; assigns a string to load, which is invalid. load('results.mat'); save; mixes load and save incorrectly.

3. Final Answer:

   load('results.mat'); -> Option D

4. Quick Check:

   Use parentheses and quotes with load [OK]

Hint: Use load('filename.mat') with quotes and parentheses [OK]

Common Mistakes:

• Omitting quotes around filename
• Using assignment instead of function call
• Mixing save and load commands

3. Consider the following MATLAB code:

x = 10; y = 20; save('mydata.mat', 'x'); clear; load('mydata.mat'); disp(y);

What will be the output?

medium

A. Error: Undefined function or variable 'y'.

B. 20

C. 10

D. No output

Solution

1. Step 1: Understand the save and clear commands

   The command save('mydata.mat', 'x') saves only variable x. The clear command removes all variables from workspace.

2. Step 2: Analyze the load and disp commands

   After load('mydata.mat'), only x is restored. Variable y is not loaded. So, disp(y) causes an error because y is undefined.

3. Final Answer:

   Error: Undefined function or variable 'y'. -> Option A

4. Quick Check:

   Only saved variables load back [OK]

Hint: Only saved variables are loaded back, others cause errors [OK]

Common Mistakes:

• Assuming all variables are saved by default
• Expecting cleared variables to still exist
• Confusing variable names in load

4. You run this MATLAB code:

save('data.mat', 'a', 'b')
clear a b
load('data.mat')

But after loading, variables a and b are missing. What is the likely problem?

medium

A. The clear command syntax is incorrect.

B. Variables a and b were never created before saving.

C. The load command is missing output arguments.

D. The file data.mat was not saved properly.

Solution

1. Step 1: Check if variables exist before saving

   If variables a and b do not exist before save, nothing is saved.

2. Step 2: Understand clear and load behavior

   clear a b removes variables a and b. Loading data.mat restores only saved variables. If none were saved, nothing loads.

3. Final Answer:

   Variables a and b were never created before saving. -> Option B

4. Quick Check:

   Save only stores existing variables [OK]

Hint: Create variables before saving to store them [OK]

Common Mistakes:

• Trying to save variables that don't exist
• Misusing clear command syntax
• Expecting load to create variables

5. You want to save multiple variables a, b, and c into a MAT file, but only if a is greater than 10. Which MATLAB code correctly does this?

hard

A. if a > 10
save('file.mat', 'a', 'b', 'c');
end

B. save('file.mat', 'a', 'b', 'c') if a > 10;

C. if (a > 10) save('file.mat', 'a', 'b', 'c'); end

D. save('file.mat', 'a', 'b', 'c') && (a > 10);

Solution

1. Step 1: Understand MATLAB if statement syntax

   MATLAB uses if condition ... end blocks. The condition must be on its own line or followed by a newline.

2. Step 2: Check each option's syntax

   if (a > 10) save('file.mat', 'a', 'b', 'c'); end uses correct one-line if syntax with parentheses and semicolon. save('file.mat', 'a', 'b', 'c') if a > 10; uses invalid inline syntax. if a > 10 save('file.mat', 'a', 'b', 'c'); end uses multiline if syntax but with newline characters which may not be valid in all contexts. save('file.mat', 'a', 'b', 'c') && (a > 10); uses invalid logical operator syntax.

3. Final Answer:

   if (a > 10) save('file.mat', 'a', 'b', 'c'); end -> Option C

4. Quick Check:

   Use proper if-end blocks or one-line if syntax in MATLAB [OK]

Hint: Use if ... end blocks or one-line if syntax for conditional save [OK]

Common Mistakes:

• Using invalid inline if syntax
• Mixing logical operators with commands
• Omitting end for if block