Local functions in MATLAB - Step-by-Step Execution

Concept Flow - Local functions

Start main function

↓

Execute main code

↓

Call local function

↓

Run local function code

↓

Return result to main

↓

Continue main or end

↓

End

The main function runs its code, calls a local function defined inside it, which executes and returns a result back to the main function.

Execution Sample

MATLAB

function result = main()
  x = 5;
  y = squareLocal(x);
  result = y;

  function y = squareLocal(n)
    y = n^2;
  end
end

This code defines a main function that calls a local function to square a number and returns the result.

Execution Table

Step	Action	Variable Values	Output/Result
1	Start main function	x: undefined, y: undefined, result: undefined
2	Assign x = 5	x: 5, y: undefined, result: undefined
3	Call local function squareLocal(5)	x: 5, y: undefined, result: undefined
4	Inside squareLocal: compute y = 5^2	n: 5, y: 25
5	Return y=25 to main	x: 5, y: 25, result: undefined
6	Assign y = 25 in main	x: 5, y: 25, result: undefined
7	Assign result = y (25)	x: 5, y: 25, result: 25
8	End main function	x: 5, y: 25, result: 25	Returns 25

💡 Main function ends after returning the result 25.

Variable Tracker

Variable	Start	After Step 2	After Step 4	After Step 6	After Step 7	Final
x	undefined	5	5	5	5	5
y	undefined	undefined	25 (local)	25	25	25
result	undefined	undefined	undefined	undefined	25	25
n (local)	undefined	undefined	5	5	5	5

Key Moments - 2 Insights

Why can't the local function squareLocal be called from outside the main function?

Because local functions in MATLAB are only visible inside the main function file after their definition, as shown in the execution_table step 3 where main calls squareLocal. Outside calls would cause an error.

Does the variable 'n' inside squareLocal affect the variable 'x' in main?

No, 'n' is local to squareLocal and separate from 'x' in main. The execution_table step 4 shows 'n' is 5 inside squareLocal, but 'x' remains 5 in main, unchanged.

Visual Quiz - 3 Questions

Look at the execution_table at step 4, what is the value of 'y' inside the local function?

A 25

B undefined

C 5

D 10

💡 Hint

Check the 'Variable Values' column at step 4 in the execution_table.

At which step does the main function assign the final result to return?

A Step 3

B Step 5

C Step 7

D Step 8

💡 Hint

Look for when 'result' gets assigned in the variable_tracker and execution_table.

If the local function was removed, what would happen at step 3?

A The program would run normally

B An error would occur because squareLocal is undefined

C The variable y would be assigned zero

D The main function would return 0

💡 Hint

Refer to the key_moments about local function visibility and step 3 in execution_table.

Concept Snapshot

Local functions in MATLAB are defined inside a main function file after the main function code.
They can only be called by the main function or other local functions in the same file.
Local functions have their own workspace and variables.
They help organize code into smaller parts.
Syntax:
function main()
  ...
  function localFunc()
    ...
  end
end

Full Transcript

This visual execution trace shows how MATLAB local functions work. The main function starts and assigns a value to x. It then calls the local function squareLocal with x as input. Inside squareLocal, the input n is squared and returned as y. The main function receives y and assigns it to result. Variables inside the local function are separate from main. The local function cannot be called from outside the main function file. This helps keep code organized and variables scoped properly.