User-defined functions in MATLAB allow users to create reusable code that can accept inputs and produce outputs. Functions are defined with specific syntax and can include multiple input and output arguments, with local variables that are only accessible within the function. Proper naming conventions and organization of function files are essential for clarity and effectiveness.

1. User Defined
Functions in MATLAB
Part 1
Shameer A Koya
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2. Introduction
O User-defined functions are similar to the
MATLAB pre-defined functions
O A function is a MATLAB program that can accept
inputs and produce outputs.
O A function can be called or executed by another
program or function.
O Code for a function is done in an Editor window
or any text editor same way as script and saved
as m-file.
O The m-file must have the same name as the
function.
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3. Introduction…
OThe convention for naming functions is the
same as for variables.
OIt is important that you give meaningful
variable names to variables inside a function
that you write, so that you and others can
understand what the function does.
OThe function M-file must be saved in your
current directory (otherwise it must be in the
path)
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4. Why use functions?
OFunctions provide reusable code
OUse same code in more than one place in
program without rewriting code
OReuse code by calling in different programs
OMake debugging easier
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5. Before you start …
OIdentify the function
ODecide the function name
ODecide the input variables
ODecide the output variables
OFile name must be the function name.
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6. Function Syntax
function[a, b, c]= basicmath(x,y)
%BASICMATH Basic Mathematical function
% basicmath(x,y) is a sample matlabfunction to perform
% basic mathematical operations on input variables x & y
% outputs of the function are sum, difference and product
% of input arguments.
a = x + y;
b = x – y;
c = x * y;
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Output arguments
Executable code
Comments about
the function
Name of the function
Input arguments
declaration
statement

7. Syntax …
O The declaration statement function is used to define the
file as a function.
O It must be typed in lower case letters.
O Input arguments
O Typed in side the parentheses ( )
O Used to transfer data into function from calling program.
O Can be zero or more input arguments.
O Output arguments
O Types inside the square brackets [ ]
O Used to transfer data out of function to calling program.
O Can be zero or more output arguments.
O Give a meaningful variable name.
O Rules for giving function name is same as the rules for
variable names.
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8. More on Function Arguments
O Functions have private workspaces
O Variables that are created inside of a user-defined
function are referred to as local variables.
O They can only be accessed from inside of that
function.
O After the function completes its operations, the
local variables are deleted from memory.
O The only variable that appears in the workspace
is the output of the function.
O Conversely, functions cannot access variables
from the workspace. (with the exception of any input
parameters they might have or “global variables”---see MATLAB
help on this matter).