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Numeric, cell arrays, matrix operations, user defined functions, programming using MATLAB; debugging MATLAB programs, applications to simulations

COM 103 ICT Applications in Food Industry (1+2)

Lecture Schedule 5 – Part - III

Dr. S. Sridevy, Ph.D.

Assistant Professor (Computer Science)

Dept. of Physical Sciences & IT

AEC&RI, TNAU, Coimbatore – 3.

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Variable Editor Window

  • Variable editor window can be opened
  • By double clicking the variable in the workspace or
  • Entering ‘var’ in command window

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User Defined Functions

  • Another type of M- file is a function file.
  • Both scripts and functions allow to reuse sequences of commands by storing them in program files.
  • Scripts are the simplest type of program, since they store commands exactly as they are typed at the command line.

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User Defined Functions (Contd.)

  • Functions provide more flexibility, primarily because functions contain sequential commands and can accept inputs and return outputs.
  • Unlike a script file, all the variables in a function file are local variables, which means their values are available only within the function.

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User Defined Functions (Contd.)

  • Function files are useful when you need to repeat a set of commands several times.
  • They are the building blocks of larger programs.
  • To create a function file, open the Editor /Debugger window

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User Defined Functions (Contd.)

  • Named functions must be defined within a program file and not at the command line.
  • The general syntax for defining a function:

function [y1,...,yN] = myfun(x1,...,xM)

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    • where y1,...,yN are outputs, x1,...,xM are inputs, and myfun is the function name.

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User Defined Functions (Contd.)

  • The first line in a function file must begin with a function definition line that has a list of inputs and outputs.
  • This line distinguishes a function M- file from a script M- file.
  • The body of a function can include valid MATLAB expressions, control flow statements, comments, blank lines, and nested functions.

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User Defined Functions (Contd.)

  • Any variables that is created within a function are stored within a workspace specific to that function, which is separate from the base workspace.
  • Functions end with either an end statement, the end of the file, or the definition line for a local function, whichever comes first.

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User Defined Functions (Contd.)

  • The end statement is required if:
    • Any function in the file contains a nested function
    • The function is a local function within a function file,
    • The function is a local function within a script file.
  • Although it is sometimes optional, use end for better code readability.

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Syntax Elaborated

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Function Keyword

  • function keyword (required)
  • Use lowercase characters for the keyword.

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Output arguments (optional)

  • If your function returns one output, you can specify the output name after the function keyword.

function myOutput = myFunction(x)

  • If your function returns more than one output, enclose the output names in square brackets.

function [one,two,three] = myFunction(x)

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Output arguments (optional)

  • If there is no output, you can omit it.

function myFunction(x)

  • Or you can use empty square brackets.

function [] = myFunction(x)

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Function name

  • Function name is required
  • Valid function names follow the same rules as variable names.
  • Function name must start with a letter, and can contain letters, digits, or underscores.

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Input arguments

  • Input arguments are optional
  • If your function accepts any inputs, enclose their names in parentheses after the function name. Separate inputs with commas.

function y = myFunction(one,two,three)

  • If there are no inputs, you can omit the parentheses.

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Example 1

  • The function named fact computes the factorial of a number (n) and returns the result (f).

function f = fact(n)

f = prod(1:n);

end

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Example 1 (Contd.)

  • Call the function from the command line

x = 5;

y = fact(5)

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y =

120

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Example 1 (Contd.)

  • Call the function from the command line
  • x = 5; y = fact(5)
  • y = 120

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Example 2

  • Starting in R2016b, another option for storing functions is to include them at the end of a script file.
  • For instance, create a file named mystats.m with a few commands and two functions, fact and perm. The script calculates the permutation of (3,2).

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Example 2 (Contd.)

x = 3;

y = 2;

z = perm(x,y)

function p = perm(n,r)

p = fact(n)*fact(n-r);

end

function f = fact(n)

f = prod(1:n);

end

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Example 2 (Contd.)

  • Call the script from the command line.

mystats

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z =

6

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Thank You!