Variable arguments (varargin, varargout) in MATLAB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is varargin in MATLAB functions?

varargin is a special input variable that allows a function to accept any number of input arguments. It collects extra inputs into a cell array.

beginner

How does varargout work in MATLAB functions?

varargout is a special output variable that allows a function to return any number of output arguments. It stores outputs in a cell array.

beginner

How do you access the third input argument passed via varargin inside a function?

You access it using varargin{3}. Since varargin is a cell array, curly braces are used to get the content.

intermediate

What happens if you request more outputs than the function provides when using varargout?

If you request more outputs than assigned in varargout, MATLAB returns empty arrays for the extra outputs.

intermediate

Why use varargin and varargout instead of fixed input/output arguments?

They make functions flexible, allowing you to handle varying numbers of inputs and outputs without rewriting the function for each case.

What type of data structure is varargin inside a MATLAB function?

A Numeric array

B Cell array

C String

D Structure

varargin collects extra inputs into a cell array, allowing different types and numbers of inputs.

How do you define a function that accepts variable input arguments in MATLAB?

A Use <code>function myFunc(input1, input2)</code>

B Use <code>function myFunc(varargout)</code>

C Use <code>function myFunc()</code>

D Use <code>function myFunc(varargin)</code>

varargin is used to accept variable input arguments.

Which syntax correctly accesses the first output argument from varargout?

A <code>varargout{1}</code>

B <code>varargout(1)</code>

C <code>varargout[1]</code>

D <code>varargout.1</code>

Since varargout is a cell array, use curly braces {} to access contents.

If a function uses varargin, what happens when you call it with no extra inputs?

A <code>varargin</code> is an empty cell array

B Error occurs

C <code>varargin</code> is <code>null</code>

D Function ignores inputs

varargin becomes an empty cell array if no extra inputs are given.

Which of these is a benefit of using varargout in a function?

A Improve function speed

B Make inputs optional

C Return a flexible number of outputs

D Automatically document outputs

varargout allows returning different numbers of outputs depending on the caller's request.

Explain how varargin and varargout work in MATLAB functions and why they are useful.

Think about how to write functions that don't have fixed numbers of inputs or outputs.

Describe how you would access the second input argument passed via varargin and the first output argument from varargout inside a MATLAB function.

Focus on the syntax for accessing cell array elements.

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