Variable arguments (varargin, varargout) in MATLAB - Mini Project: Build & Apply

Variable arguments (varargin, varargout) in MATLAB

📖 Scenario: You are creating a MATLAB function that can accept a flexible number of input arguments and return a flexible number of output arguments. This is useful when you want to write a function that can handle different numbers of inputs and outputs without errors.

🎯 Goal: Build a MATLAB function called flexibleSum that uses varargin to accept any number of numeric inputs and returns their sum. Also, use varargout to optionally return the count of inputs and the average of the inputs as additional outputs.

📋 What You'll Learn

Create a function flexibleSum that uses varargin to accept variable inputs

Calculate the sum of all numeric inputs

Use varargout to optionally return the count of inputs and the average

Test the function with different numbers of inputs and outputs

💡 Why This Matters

🌍 Real World

Functions with variable arguments are useful in real-world MATLAB projects where the number of inputs or outputs can change, such as data analysis tools or flexible calculators.

💼 Career

Knowing how to use <code>varargin</code> and <code>varargout</code> is important for MATLAB programmers working in engineering, research, or data science roles where flexible functions improve code reuse and robustness.

1

Create the function header with varargin

Write the first line of the function flexibleSum that accepts variable input arguments using varargin.

MATLAB

% Create the function header with varargin
function total = flexibleSum(varargin)
% Your code here

Hint

Use function keyword and varargin to accept any number of inputs.

2

Calculate the sum of all inputs

Inside the function, create a variable total that sums all numeric values in varargin using a for loop.

MATLAB

function total = flexibleSum(varargin)
% Initialize total
% Your code here

Hint

Start total at 0 and add each input from varargin inside a loop.

3

Add varargout to return count and average

Modify the function header to include varargout. Inside the function, set varargout{1} to the number of inputs and varargout{2} to the average of inputs if requested.

MATLAB

function [total, varargout] = flexibleSum(varargin)
    total = 0;
    for k = 1:length(varargin)
        total = total + varargin{k};
    end
    % Your code here to set varargout

Hint

Use nargout to check how many outputs are requested and assign varargout accordingly.

4

Test the function and display outputs

Call flexibleSum with inputs 10, 20, 30 and capture all three outputs: total, count, and average. Then, use disp to print each output on a separate line.

MATLAB

% Call flexibleSum with 10, 20, 30 and capture outputs
% Your code here

Hint

Use square brackets to capture multiple outputs and disp to show them.

Practice

1. What does varargin do in a MATLAB function?

easy

A. Returns multiple output arguments as a cell array

B. Collects all input arguments into a cell array

C. Limits the number of input arguments to one

D. Specifies the data type of input arguments

Solution

1. Step 1: Understand the role of varargin

   varargin is used to collect any number of input arguments passed to a function into a single cell array.

2. Step 2: Differentiate from varargout

   varargout is used for output arguments, not input. So it does not collect inputs.

3. Final Answer:

   Collects all input arguments into a cell array -> Option B

4. Quick Check:

   varargin = input collector [OK]

Hint: Remember: 'varargin' collects inputs, 'varargout' returns outputs [OK]

Common Mistakes:

• Confusing varargin with varargout
• Thinking varargin limits inputs
• Assuming varargin specifies data types

2. Which of the following is the correct way to define a MATLAB function that accepts a fixed input followed by any number of additional inputs using varargin?

easy

A. function output = myFunc(input1, varargin)

B. function output = myFunc(varargout)

C. function output = myFunc(varargin)

D. function output = myFunc(varargin, input1)

Solution

1. Step 1: Check correct varargin placement

   varargin must be the last input argument to collect all remaining inputs.

2. Step 2: Evaluate options

   function output = myFunc(input1, varargin): function output = myFunc(input1, varargin) correctly places varargin after the fixed input input1. function output = myFunc(varargout) incorrectly uses varargout as an input. function output = myFunc(varargin) has no fixed input. function output = myFunc(varargin, input1) places varargin before a fixed input, which is invalid.

3. Final Answer:

   function output = myFunc(input1, varargin) -> Option A

4. Quick Check:

   varargin must be last input [OK]

Hint: Put varargin last in input list to accept extra arguments [OK]

Common Mistakes:

• Placing varargin before fixed inputs
• Using varargout as input
• Omitting parentheses in function definition

3. What will be the output of the following MATLAB code?

function varargout = exampleFunc(varargin)
  n = length(varargin);
  for k = 1:n
    varargout{k} = varargin{k} * 2;
  end
end

[a, b] = exampleFunc(3, 5); disp([a, b]);

medium

A. Error: varargout not assigned properly

B. [3 5]

C. [6 10]

D. [9 25]

Solution

1. Step 1: Understand varargin and varargout usage

   varargin collects inputs {3, 5}. The loop doubles each input and assigns to varargout.

2. Step 2: Calculate output values

   3 * 2 = 6, 5 * 2 = 10. So outputs are 6 and 10.

3. Final Answer:

   [6 10] -> Option C

4. Quick Check:

   Each input doubled = output [OK]

Hint: varargin inputs, varargout outputs; loop doubles inputs here [OK]

Common Mistakes:

• Confusing input and output values
• Forgetting to assign varargout elements
• Assuming varargout is a numeric array, not cell

4. Identify the error in this MATLAB function using varargin:

function result = sumAll(varargin)
  total = 0;
  for i = 1:varargin
    total = total + varargin{i};
  end
  result = total;
end

medium

A. Incorrect indexing of varargin with parentheses

B. Missing output argument varargout

C. No error, function works correctly

D. Using varargin as a number in the for loop

Solution

1. Step 1: Check for loop range

   The for loop uses 1:varargin, but varargin is a cell array, not a number.

2. Step 2: Correct way to get number of inputs

   Use length(varargin) or nargin to get number of inputs for the loop.

3. Final Answer:

   Using varargin as a number in the for loop -> Option D

4. Quick Check:

   Loop needs numeric length, not cell array [OK]

Hint: Use length(varargin) to loop over inputs, not varargin itself [OK]

Common Mistakes:

• Using varargin directly as a number
• Forgetting to use curly braces for cell access
• Assuming varargout is required for outputs

5. You want to write a MATLAB function that accepts any number of numeric inputs and returns their squares as multiple outputs. Which function definition and body correctly uses varargin and varargout to achieve this?

hard

A. function varargout = squareAll(varargin)
for k = 1:length(varargin)
varargout{k} = varargin{k}^2;
end
end

B. function varargout = squareAll(varargin)
for k = 1:nargin
varargout{k} = varargin(k)^2;
end
end

C. function varargout = squareAll(varargin)
for k = 1:length(varargin)
varargout(k) = varargin{k}^2;
end
end

D. function varargout = squareAll(varargin)
for k = 1:nargout
varargout{k} = varargin{k}^2;
end
end

Solution

1. Step 1: Check input count method

   Using length(varargin) correctly gets the number of inputs. nargin inside the function counts all inputs including fixed ones, but here only varargin inputs matter.

2. Step 2: Check cell indexing and assignment

   Accessing inputs with varargin{k} and assigning outputs with varargout{k} using curly braces is correct. Parentheses would cause errors.

3. Final Answer:

   function varargout = squareAll(varargin) for k = 1:length(varargin) varargout{k} = varargin{k}^2; end end -> Option A

4. Quick Check:

   Use length(varargin) and curly braces for cell access [OK]

Hint: Use length(varargin) and curly braces {} for cell arrays [OK]

Common Mistakes:

• Using parentheses instead of curly braces for cell access
• Using nargin instead of length(varargin)
• Assigning outputs with parentheses instead of curly braces