matlab class assignment operator

In many cases, you may want to change the behavior of the MATLAB operators and functions for cases when the arguments are objects. You can accomplish this by overloading the relevant functions. Overloading enables a function to handle different types and numbers of input arguments and perform whatever operation is appropriate for the highest-precedence object. See Object Precedence for more information on object precedence.

Each built-in MATLAB operator has an associated function name (e.g., the + operator has an associated plus.m function). You can overload any operator by creating an M-file with the appropriate name in the class directory. For example, if either p or q is an object of type class_name , the expression

generates a call to a function @ class_name /plus.m , if it exists. If p and q are both objects of different classes, then MATLAB applies the rules of precedence to determine which method to use.

See the following sections for examples of overloaded operators:

• Overloading the + Operator
• Overloading the - Operator
• Overloading the * Operator

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1.1: Operators and Special Characters

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Creating a Simple Class

Design class.

The basic purpose of a class is to define an object that encapsulates data and the operations performed on that data. For example, BasicClass defines a property and two methods that operate on the data in that property:

Value — Property that contains the numeric data stored in an object of the class

roundOff — Method that rounds the value of the property to two decimal places

multiplyBy — Method that multiplies the value of the property by the specified number

Start a class definition with a classdef ClassName ...end block, and then define the class properties and methods inside that block. Here is the definition of BasicClass :

For a summary of class syntax, see classdef .

To use the class:

Save the class definition in a .m file with the same name as the class.

Create an object of the class.

Access the properties to assign data.

Call methods to perform operation on the data.

Create Object

Create an object of the class using the class name:

Initially, the property value is empty.

Access Properties

Assign a value to the Value property using the object variable and a dot before the property name:

To return a property value, use dot notation without the assignment:

For information on class properties, see Property Syntax .

Call Methods

Call the roundOff method on object a :

Pass the object as the first argument to a method that takes multiple arguments, as in this call to the multiplyBy method:

You can also call a method using dot notation:

Passing the object as an explicit argument is not necessary when using dot notation. The notation uses the object to the left of the dot.

For information on class methods, see Method Syntax .

Add Constructor

Classes can define a special method to create objects of the class, called a constructor. Constructor methods enable you to pass arguments to the constructor, which you can assign as property values. The BasicClass Value property restricts its possible values using the mustBeNumeric function.

Here is a constructor for the BasicClass class. When you call the constructor with an input argument, it is assigned to the Value property. If you call the constructor without an input argument, the Value property has a default value of empty ( [] ).

By adding this constructor to the class definition, you can create an object and set the property value in one step:

The constructor can perform other operations related to creating objects of the class.

For information on constructors, see Class Constructor Methods .

Vectorize Methods

MATLAB ® enables you to vectorize operations. For example, you can add a number to a vector:

MATLAB adds the number 2 to each of the elements in the array [1 2 3] . To vectorize the arithmetic operator methods, enclose the obj.Value property reference in brackets.

This syntax enables the method to work with arrays of objects. For example, create an object array using indexed assignment.

These two expressions are equivalent.

The roundOff method is vectorized because the property reference is enclosed in brackets. r = round([obj.Value],2); Because roundOff is vectorized, it can operate on arrays.

Overload Functions

Classes can implement existing functionality, such as addition, by defining a method with the same name as the existing MATLAB function. For example, suppose that you want to add two BasicClass objects. It makes sense to add the values of the Value properties of each object.

Here is an overloaded version of the MATLAB plus function. It defines addition for the BasicClass class as adding the property values:

By implementing a method called plus , you can use the “ + ” operator with objects of BasicClass .

By vectorizing the plus method, you can operate on object arrays. a = BasicClass(pi/3); b = BasicClass(pi/4); c = BasicClass(pi/2); ar = [a b]; ar + c ans = 2.6180 2.3562

Related Information

For information on overloading functions, see Overload Functions in Class Definitions .

For information on overloading operators, see Operator Overloading .

BasicClass Code Listing

Here is the BasicClass definition after adding the features discussed in this topic:

Related Topics

• Components of a Class
• Validate Property Values

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Creating a Simple Class

Design class.

The basic purpose of a class is to define an object that encapsulates data and the operations performed on that data. For example, BasicClass defines a property and two methods that operate on the data in that property:

Value — Property that contains the numeric data stored in an object of the class

roundOff — Method that rounds the value of the property to two decimal places

multiplyBy — Method that multiplies the value of the property by the specified number

Start a class definition with a classdef ClassName ...end block, and then define the class properties and methods inside that block. Here is the definition of BasicClass :

For a summary of class syntax, see classdef .

To use the class:

Save the class definition in a .m file with the same name as the class.

Create an object of the class.

Access the properties to assign data.

Call methods to perform operation on the data.

Create Object

Create an object of the class using the class name:

Initially, the property value is empty.

Access Properties

Assign a value to the Value property using the object variable and a dot before the property name:

To return a property value, use dot notation without the assignment:

For information on class properties, see Property Syntax .

Call Methods

Call the roundOff method on object a :

Pass the object as the first argument to a method that takes multiple arguments, as in this call to the multiplyBy method:

You can also call a method using dot notation:

Passing the object as an explicit argument is not necessary when using dot notation. The notation uses the object to the left of the dot.

For information on class methods, see Method Syntax .

Add Constructor

Classes can define a special method to create objects of the class, called a constructor. Constructor methods enable you to pass arguments to the constructor, which you can assign as property values. The BasicClass Value property restricts its possible values using the mustBeNumeric function.

Here is a constructor for the BasicClass class. When you call the constructor with an input argument, it is assigned to the Value property. If you call the constructor without an input argument, the Value property has a default value of empty ( [] ).

By adding this constructor to the class definition, you can create an object and set the property value in one step:

The constructor can perform other operations related to creating objects of the class.

For information on constructors, see Class Constructor Methods .

Vectorize Methods

MATLAB ® enables you to vectorize operations. For example, you can add a number to a vector:

MATLAB adds the number 2 to each of the elements in the array [1 2 3] . To vectorize the arithmetic operator methods, enclose the obj.Value property reference in brackets.

This syntax enables the method to work with arrays of objects. For example, create an object array using indexed assignment.

These two expressions are equivalent.

The roundOff method is vectorized because the property reference is enclosed in brackets. r = round([obj.Value],2); Because roundOff is vectorized, it can operate on arrays.

Overload Functions

Classes can implement existing functionality, such as addition, by defining a method with the same name as the existing MATLAB function. For example, suppose that you want to add two BasicClass objects. It makes sense to add the values of the Value properties of each object.

Here is an overloaded version of the MATLAB plus function. It defines addition for the BasicClass class as adding the property values:

By implementing a method called plus , you can use the “ + ” operator with objects of BasicClass .

By vectorizing the plus method, you can operate on object arrays. a = BasicClass(pi/3); b = BasicClass(pi/4); c = BasicClass(pi/2); ar = [a b]; ar + c ans = 2.6180 2.3562

Related Information

For information on overloading functions, see Overload Functions in Class Definitions .

For information on overloading operators, see Operator Overloading .

BasicClass Code Listing

Here is the BasicClass definition after adding the features discussed in this topic:

Related Topics

• Components of a Class
• Validate Property Values

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how can I do a *= operator in matlab

I'm trying to do in Matlab: X = X*-1;

this syntax is a bit annoying, is there a way to do this some other way (like in c++ : x*=-1)

• matlab-guide

• 1 AFAIK the answer is NO ! –  P0W Nov 30, 2013 at 16:01
• 2 Related (if not possibly duplicate): What is the equivalent to += in MATLAB? . Matlab does not support compound assignment operators . –  horchler Nov 30, 2013 at 16:28

2 Answers 2

Unfortunately there are no increment and compound assignment operators in Matlab. I also remember reading posts by employees at Mathworks saying that they don't intend to add such operators to Matlab.

Steve Lord's reply to the following question illustrates the difficulties involved (way down, reply nr 10 or so): http://www.mathworks.com/matlabcentral/newsreader/view_thread/107451

• The link is down, "As of December 2017 the Newsreader application has been shut down." May I know his reply? –  Unknown123 Nov 20, 2018 at 9:47
• @Unknown123 Wayback Machine has a snapshot –  Ruslan Nov 6, 2021 at 8:41

There is another way! ;-)

Seriously though, I think it's just a matter of habit. There's nothing inherently wrong with that syntax, you are just used to do it differently.

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Operators and Elementary Operations

The MATLAB ® language uses many common operators and special characters that you can use to perform simple operations on arrays of any type. See MATLAB Operators and Special Characters for a comprehensive summary.

Operator Basics

• MATLAB Operators and Special Characters
• Operator Precedence
• Array vs. Matrix Operations
• Compatible Array Sizes for Basic Operations
• Arithmetic Operations Addition, subtraction, multiplication, division, power, rounding
• Relational Operations Value comparisons
• Logical (Boolean) Operations True or false conditions
• Set Operations Unions, intersection, set membership
• Bit-Wise Operations Set, shift, or compare specific bit fields

MATLAB Command

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Run the command by entering it in the MATLAB Command Window. Web browsers do not support MATLAB commands.

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