Input and output arguments in MATLAB - Step-by-Step Execution

Concept Flow - Input and output arguments

Function called with inputs

↓

Inputs assigned to input args

↓

Function body executes

↓

Output args assigned values

↓

Function returns outputs

↓

Outputs received by caller

This flow shows how inputs enter a function, the function runs, and outputs are sent back to the caller.

Execution Sample

MATLAB

function [sum, diff] = add_sub(a, b)
  sum = a + b;
  diff = a - b;
end

[x, y] = add_sub(5, 3);

This function takes two inputs, returns their sum and difference, and the caller receives both outputs.

Execution Table

Step	Action	Input Arguments	Output Arguments	Notes
1	Function called	a=5, b=3	sum=?, diff=?	Inputs assigned to a and b
2	Calculate sum	a=5, b=3	sum=8, diff=?	sum = 5 + 3 = 8
3	Calculate diff	a=5, b=3	sum=8, diff=2	diff = 5 - 3 = 2
4	Function ends	a=5, b=3	sum=8, diff=2	Outputs ready to return
5	Outputs assigned	N/A	x=8, y=2	Caller receives outputs
6	Execution complete	N/A	x=8, y=2	Function finished

💡 Function completes after assigning outputs and returning to caller

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
a	undefined	5	5	5
b	undefined	3	3	3
sum	undefined	8	8	8
diff	undefined	undefined	2	2
x	undefined	undefined	undefined	8
y	undefined	undefined	undefined	2

Key Moments - 3 Insights

Why do we assign inputs to variables 'a' and 'b' inside the function?

Because when the function is called (see Step 1 in execution_table), the input values are passed and assigned to the input argument variables 'a' and 'b' so the function can use them.

How does the function return two outputs?

The function assigns values to the output variables 'sum' and 'diff' inside (Steps 2 and 3), then these are returned to the caller and assigned to 'x' and 'y' (Step 5).

What happens if the caller requests fewer outputs than the function provides?

If fewer outputs are requested, MATLAB assigns only those outputs and ignores the rest. This is not shown here but is important to know.

Visual Quiz - 3 Questions

Look at the execution_table at Step 3, what is the value of 'diff'?

A 3

B 2

C 8

D undefined

💡 Hint

Check the 'Output Arguments' column at Step 3 in the execution_table.

At which step does the function assign the input values to variables 'a' and 'b'?

A Step 1

B Step 4

C Step 2

D Step 5

💡 Hint

Look at the 'Action' and 'Notes' columns in the execution_table for when inputs are assigned.

If the caller only requested one output, how would the variable_tracker change for 'y'?

A 'y' would be 8

B 'y' would be 2

C 'y' would be undefined or not assigned

D 'y' would be equal to 'x'

💡 Hint

Recall that outputs not requested by the caller are not assigned (see key_moments about output count).

Concept Snapshot

MATLAB functions receive inputs as arguments and return outputs.
Syntax: function [out1, out2] = func(in1, in2)
Inputs are assigned to input variables when called.
Outputs are assigned inside and returned to caller.
Caller receives outputs in order requested.
If fewer outputs requested, extra outputs are ignored.

Full Transcript

This visual trace shows how MATLAB functions handle input and output arguments. When the function is called, the input values are assigned to the input variables inside the function. The function then runs its code, calculating outputs by assigning values to output variables. Finally, these outputs are returned to the caller and assigned to variables there. The execution table steps through each action, showing variable values changing. Key moments clarify common confusions about input assignment and output return. The quiz tests understanding of variable values at different steps and the effect of requesting fewer outputs. This helps beginners see clearly how data flows into and out of MATLAB functions.

Practice

1. What is the main purpose of input arguments in a MATLAB function?

easy

A. To send data into the function for processing

B. To display results on the screen

C. To store variables permanently

D. To create new functions inside the main function

Solution

1. Step 1: Understand input arguments

   Input arguments are values or data you give to a function so it can use them inside.

2. Step 2: Identify the purpose

   The main purpose is to send data into the function for it to work on.

3. Final Answer:

   To send data into the function for processing -> Option A

4. Quick Check:

   Input arguments = send data in [OK]

Hint: Input arguments bring data into functions [OK]

Common Mistakes:

• Confusing input arguments with output arguments
• Thinking input arguments display results
• Assuming input arguments create new functions

2. Which of the following is the correct syntax to define a MATLAB function with one input and one output argument?

easy

A. function output = myFunc(input)

B. function myFunc(input) = output

C. function (output) = myFunc input

D. function myFunc output(input)

Solution

1. Step 1: Recall MATLAB function syntax

   The correct syntax starts with 'function', then output, '=', function name, and input in parentheses.

2. Step 2: Match the syntax

   function output = myFunc(input) matches this pattern exactly: function output = myFunc(input)

3. Final Answer:

   function output = myFunc(input) -> Option A

4. Quick Check:

   Syntax = function output = name(input) [OK]

Hint: Output = functionName(input) is the right order [OK]

Common Mistakes:

• Placing output after function name without '='
• Missing parentheses around input
• Using '=' incorrectly in function header

3. What will be the output of the following MATLAB function call?

function y = squarePlusOne(x)
    y = x^2 + 1;
end

result = squarePlusOne(3);

medium

A. 9

B. 10

C. 7

D. 16

Solution

1. Step 1: Calculate the square of input

   Input x is 3, so x^2 = 3^2 = 9.

2. Step 2: Add 1 to the squared value

   9 + 1 = 10.

3. Final Answer:

   10 -> Option B

4. Quick Check:

   3 squared plus 1 = 10 [OK]

Hint: Square input, then add one [OK]

Common Mistakes:

• Forgetting to add 1 after squaring
• Using multiplication instead of power
• Confusing output with input

4. Identify the error in this MATLAB function definition:

function output = addNumbers(a, b)
    output = a + b
end

medium

A. Input arguments must be in square brackets

B. Function name should be capitalized

C. Output variable cannot be named 'output'

D. Missing semicolon after output assignment

Solution

1. Step 1: Check MATLAB syntax rules

   Each statement should end with a semicolon to suppress output in functions.

2. Step 2: Identify missing semicolon

   The line 'output = a + b' lacks a semicolon at the end.

3. Final Answer:

   Missing semicolon after output assignment -> Option D

4. Quick Check:

   Statements need semicolons [OK]

Hint: End statements with semicolon inside functions [OK]

Common Mistakes:

• Ignoring semicolon causes unwanted output
• Thinking function names must be capitalized
• Using wrong brackets for inputs

5. You want to write a MATLAB function that takes two numbers as input and returns both their sum and product as outputs. Which function header is correct?

hard

A. function sum, product = calculate(a, b)

B. function calculate(a, b) = [sum, product]

C. function [sum, product] = calculate(a, b)

D. function calculate = [sum, product](a, b)

Solution

1. Step 1: Recall syntax for multiple outputs

   Multiple outputs are enclosed in square brackets before the '=' sign.

2. Step 2: Match correct syntax

   function [sum, product] = calculate(a, b) uses square brackets for outputs and correct order: function [sum, product] = calculate(a, b)

3. Final Answer:

   function [sum, product] = calculate(a, b) -> Option C

4. Quick Check:

   Multiple outputs use square brackets [OK]

Hint: Use square brackets for multiple outputs [OK]

Common Mistakes:

• Omitting square brackets for multiple outputs
• Placing outputs after function name without brackets
• Using '=' incorrectly in function header