COMPLETE GUIDE TO MATLAB ®

Chapter 3 : Types of Functions

Types of Functions

Chapter Outline

• Nested functions

• Private functions

• Overloaded functions

• Function handles

Types of Functions

function T = tax(income)

adjusted_income = max(income - 5000, 0);T = compute_tax;

function t = compute_tax t = 0.28*adjusted_income; end

end

%call function%tax(10000)

function T = tax(income)

adjusted_income = max(income - 5000, 0);T = compute_tax;

function t = compute_tax t = 0.28*adjusted_income; end

end

%call function%tax(10000)

Nested Function

Types of Functions

Private Functions• Reside in a subdirectory named private

• Only accessible to functions in parent directory

Only accessible to functions inparent directory.

privatedirectory

Types of Functions

Chapter Outline

• Nested functions

• Private functions

• Function handles

Types of Functions

Object Oriented Programming (OOPs) in MATLABWhat is Object-Oriented Programming?

Helps you work on big projects which has activities/elements with properties that can be grouped in a structured way

What are operations and how do I perform them?

1) First define the elements – class2) Define the properties of the class3) Define methods – constructor for creating new

objects/elements/activities4) Other Methods are defined to manipulate the input

data

Types of Functions

Classes

In class definition we create a prototype or specification for construction of a objects of a certain class or type.

Eg. classdef person

Objects

Run-time instance of a class

Object Oriented Programming

PropertiesList of properties by which the class is desired to be

characterized

Types of Functions

classdef Personpropertiesnameagegenderendmethods

function obj=Person(name,age,gender)obj.name=name;obj.age=age;obj.gender=gender;

End

function y=isRetired(obj) y=obj.age > 65;end

endend

Types of Functions

>> x=Person('john',35,'male') x = Person Properties: name: 'john' age: 35 gender: 'male' Methods

>> x.isRetired ans =  0

Types of Functions

Exercise

Extend the Person class with a list of book numbers that a person borrowed and the method holdsBook to check whether a person has borrowed a particular book. Check your class with the

commands:

x=Person('John',35,'male');

x.books=[1 2 3 4];

x.holdsBook(3)

Access to object properties

x=Person('John',35,'male');

x.age=70;

x.isRetired

returns ‘1’

Types of Functions

Use ‘handle’ to pass class – person as reference not a value.

classdef Person < handle

function changeAge(obj,age)

obj.age=age;

end

>>x=Person('John',35,'male');

>>x.changeAge(70);

>>x.age

Types of Functions

classdef date % write a description of the class here. properties % define the properties of the class here, (like fields of a struct) minute = 0; %calcSecs(d2) hour; day; month; year; end properties(Constant = true) DAYS_PER_YEAR = 365; MONTHS_PER_YEAR = 12; WEEKS_PER_YEAR = 52; end Methods (Access=public) % Change to private and run % methods, including the constructor are defined in this block function obj = date(minute,hour,day,month,year) % class constructor if(nargin > 0) obj.minute = minute; obj.hour = hour; obj.day = day; obj.month = month; obj.year = year; end end function obj = rollDay(obj,numdays) obj.day = obj.day + numdays; endend end

Types of Functions

……..Contd

Create Object

>>d1=date(0,3,27,2,1998)>>d2=date(1,0,0,0,2002)

Properties

>>day =d1.day %Access the day property>>d1.year=2008; %Set the year property

Methods

>>d1=rollDay(d1,3) % rollDay methods adds a specified number of days to the day property

Exercise

Add the following methods

function sec=calcSecs(obj) sec=obj.minute*60 + obj.hour*60*60+obj.day*24*60*60;end

And calculate secs for object date 1 min.

1st argument is the object of the class

Types of Functions

feval Function

• Syntax

• If function is a quoted string containing the name of a function (usually defined by an M-file), then feval(function,x1,...,xn) evaluates the function with the given arguments.

[y1,y2,...] = feval(function,x1,...,xn)[y1,y2,...] = feval(function,x1,...,xn)

>> x = 0:.1:2*pi;>> y = feval('sin', 0:.1:2*pi);>> plot(x,y)

>> x = 0:.1:2*pi;>> y = feval('sin', 0:.1:2*pi);>> plot(x,y)

Types of Functions

Representing Mathematical Functions

• A mathematical function can be represented in MATLAB as a function

function y = my_humps(x)y = 1 ./ ((x-.3).^2 + .01) + 1 ./ ((x-.9).^2 + .04) - 6;

function y = my_humps(x)y = 1 ./ ((x-.3).^2 + .01) + 1 ./ ((x-.9).^2 + .04) - 6;

6-0.040.9)-(x

1

01.0.3)-(x

1 F(x)

22

Types of Functions

Function Handles

• What are they?

• MATLAB data types that contain information used in referencing a function.

• Benefits:

• Allow wider access to subfunctions and private functions.

• Improve performance in repeated operations.

• Reduce the number of files that define your function.

• Ensure reliability when evaluating functions.

Types of Functions

Function Handles – continued• Syntax

• fhandle = @function_name

• Example

function y = my_humps(x)y = 1 ./ ((x-.3).^2 + .01) + 1 ./ ((x-.9).^2 + .04) - 6;% ----- end of file my_humps.m -----

>> x = 0:.1:2; >> fhandle = @my_humps;>> out = feval(fhandle,x); % or… out = feval('my_humps',x);>> plot(x,out);

function y = my_humps(x)y = 1 ./ ((x-.3).^2 + .01) + 1 ./ ((x-.9).^2 + .04) - 6;% ----- end of file my_humps.m -----

>> x = 0:.1:2; >> fhandle = @my_humps;>> out = feval(fhandle,x); % or… out = feval('my_humps',x);>> plot(x,out);

Types of Functions

Function Handles – continued

• The command functions allows the function handle information to be displayed.

• This function is helpful when working with overloaded function handles.

>> fhandle = @my_humps;>> functions(fhandle)ans = function: 'my_humps' type: 'simple' file: 'c:\class\my_humps.m'

>> fhandle = @my_humps;>> functions(fhandle)ans = function: 'my_humps' type: 'simple' file: 'c:\class\my_humps.m'

Types of Functions

Function Handle Operations

• Converting function handle to function name

• Converting function name to function handle

>> fhandle = @sin;>> func2str(fhandle)ans =sin

>> fhandle = @sin;>> func2str(fhandle)ans =sin

>> fh = str2func('sin')fh = @sin

>> fh = str2func('sin')fh = @sin

Types of Functions

Section Summary• Nested Function

• Private Function

• Objects in MATLAB

• Constructing a new class

• Function precedence

• Function Handles