Workspace and variable management in MATLAB - Step-by-Step Execution

Concept Flow - Workspace and variable management

Start MATLAB session

↓

Create variables

↓

Variables stored in Workspace

↓

Use variables in commands/functions

↓

Modify or clear variables

↓

Workspace updated

↓

End or save session

This flow shows how variables are created, stored, used, modified, and cleared in the MATLAB workspace during a session.

Execution Sample

MATLAB

a = 5;
b = 10;
c = a + b;
clear a;
disp(who);

This code creates variables a, b, c, clears a, and then displays remaining variables in the workspace.

Execution Table

Step	Command	Workspace Variables	Action	Output
1	a = 5;	a	Create variable a with value 5
2	b = 10;	a, b	Create variable b with value 10
3	c = a + b;	a, b, c	Create c as sum of a and b (15)
4	clear a;	b, c	Remove variable a from workspace
5	disp(who);	b, c	Display variables currently in workspace	b c

💡 End of commands; workspace contains variables b and c only.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	Final
a	undefined	5	5	5	cleared	cleared
b	undefined	undefined	10	10	10	10
c	undefined	undefined	undefined	15	15	15

Key Moments - 2 Insights

Why does variable 'a' disappear after the 'clear a;' command?

The 'clear a;' command removes 'a' from the workspace, so it no longer exists after step 4, as shown in the execution_table row 4.

What does the 'who' function show after clearing 'a'?

The 'who' function lists all variables currently in the workspace. After clearing 'a', it shows only 'b' and 'c' as in execution_table row 5.

Visual Quiz - 3 Questions

Look at the execution_table at step 3. What is the value of variable 'c'?

A 5

B 15

C 10

D undefined

💡 Hint

Check the 'Workspace Variables' and 'Action' columns at step 3 in the execution_table.

At which step does variable 'a' get removed from the workspace?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Command' and 'Workspace Variables' columns in the execution_table.

If we did not run 'clear a;', what would 'who' display at step 5?

A a, b, c

B b, c

C a, c

D a, b

💡 Hint

Compare the workspace variables before and after the 'clear a;' command in the execution_table.

Concept Snapshot

Workspace and variable management in MATLAB:
- Variables are created by assignment (e.g., a = 5;).
- Variables live in the workspace until cleared or session ends.
- Use 'clear varname;' to remove variables.
- Use 'who' to list current workspace variables.
- Variables can be used and modified anytime during the session.

Full Transcript

This lesson shows how MATLAB manages variables in its workspace. When you assign a value to a variable, it appears in the workspace. You can use these variables in calculations or commands. If you want to remove a variable, use the 'clear' command with the variable name. The 'who' command lists all variables currently stored. This helps you keep track of what data you have while working. The example code creates three variables, clears one, and then shows the remaining variables. This process helps you manage your workspace efficiently.

Practice

1. What does the clear command do in MATLAB workspace?

easy

A. Removes variables from the workspace

B. Displays all variables in the workspace

C. Saves variables to a file

D. Loads variables from a file

Solution

1. Step 1: Understand the purpose of clear

   The clear command is used to remove variables from the workspace, freeing memory.

2. Step 2: Differentiate from other commands

   who and whos display variables, save saves variables, and load loads variables.

3. Final Answer:

   Removes variables from the workspace -> Option A

4. Quick Check:

   clear removes variables [OK]

Hint: Clear removes variables, not shows or saves [OK]

Common Mistakes:

• Confusing clear with who or whos
• Thinking clear saves variables
• Assuming clear loads variables

2. Which of the following is the correct syntax to list all variables in the workspace with details?

easy

A. listvars

B. whos

C. showvars()

D. vars()

Solution

1. Step 1: Recall commands to list variables

   who lists variable names; whos lists variables with details like size and type.

2. Step 2: Identify correct syntax

   whos is the correct command; others are invalid or do not exist in MATLAB.

3. Final Answer:

   whos -> Option B

4. Quick Check:

   whos lists variables with details [OK]

Hint: Use whos to see detailed variable info [OK]

Common Mistakes:

• Using non-existent commands like listvars
• Confusing who with whos for details
• Adding parentheses to whos (it's not a function)

3. Consider the following MATLAB commands:

a = 5;
b = 10;
clear a;
whos

What variables will whos display?

medium

A. No variables

B. Only a

C. a and b

D. Only b

Solution

1. Step 1: Analyze the commands

   Variables a and b are created. Then clear a removes a from workspace.

2. Step 2: Determine remaining variables

   After clearing a, only b remains. whos will show b only.

3. Final Answer:

   Only b -> Option D

4. Quick Check:

   clear a removes a, so only b remains [OK]

Hint: Clear specific variable removes only that variable [OK]

Common Mistakes:

• Assuming clear removes all variables
• Thinking clear a clears variable b too
• Expecting whos to show cleared variables

4. What is wrong with this MATLAB code snippet?

clear x y
x = 10;
load('data.mat')

Assuming data.mat contains variable y with value 5.

medium

A. clear cannot take multiple variables

B. No error, code works as expected

C. load overwrites variable y after clear

D. Variable x is cleared after load

Solution

1. Step 1: Understand clear and load behavior

   clear x y removes variables x and y. Then x is assigned 10.

2. Step 2: Effect of load on variables

   load('data.mat') loads variable y from file, overwriting any existing y. Since y was cleared, it is now restored from file.

3. Step 3: Identify the issue

   The variable y is overwritten by load, which may be unexpected if user thought clear removed it permanently.

4. Final Answer:

   load overwrites variable y after clear -> Option C

5. Quick Check:

   load restores variables from file, overwriting workspace [OK]

Hint: Load restores variables, overwriting existing ones [OK]

Common Mistakes:

• Thinking clear cannot clear multiple variables
• Assuming load does not overwrite variables
• Believing x is cleared after load

5. You want to save only variables a and b from your workspace to a file named myvars.mat. Which command should you use?

hard

A. save myvars.mat a b

B. save('myvars.mat', 'a', b)

C. save('myvars.mat')

D. save('myvars.mat', a, b)

Solution

1. Step 1: Recall save syntax for specific variables

   To save specific variables, list their names without quotes after the filename without parentheses.

2. Step 2: Analyze options

   save myvars.mat a b uses correct syntax: save myvars.mat a b. save('myvars.mat', 'a', b) uses quotes but parentheses, which is invalid syntax in MATLAB. save('myvars.mat') saves all variables. save('myvars.mat', a, b) passes variables as values, which is incorrect.

3. Final Answer:

   save myvars.mat a b -> Option A

4. Quick Check:

   Use save filename var1 var2 to save specific variables [OK]

Hint: Use save filename var1 var2 without parentheses [OK]

Common Mistakes:

• Using parentheses with save command
• Putting variable names in quotes inside parentheses
• Saving all variables unintentionally