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.