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Simulink 3D Animation 10 Pages. Gauges Blockset 2 Pages. Simulink Report Generator 3 Pages. Polyspace Bug Finder 6 Pages. Phased Array System Toolbox 9 Pages.
OPC Toolbox 5 Pages. Simulink Design Verifier 7 Pages. Simulink Design Optimization 10 Pages. Bioinformatics Toolbox 9 Pages. SimBiology 6 Pages. Computer Vision System Toolbox 10 Pages. Fuzzy Logic Toolbox 5 Pages. System Identification Toolbox 6 Pages. Partial Differential Equation Toolbox 5 Pages. SimMechanics 7 Pages.
Simscape 7 Pages. Simulink 6 Pages. Data Acquisition Toolbox 8 Pages. Image Processing Toolbox 7 Pages. We could create structs with minute, hour, day, month, and year fields and store all of the information about specific dates and times in these. This would certainly be better than having separate variables for all of these values floating around unstructured.
However, there are also a number of operations we might want to perform on these dates, such as incrementing them by a day, comparing them, subtracting them, etc. We could write stand alone functions to perform all of these operations, but it would be nice to organize them together too, just as we did the data. This is precisely what an object oriented approach lets us do. There are further differences and advantages, which we will come to in due course. We first describe how to write a class definition.
If you are new to OOP, make sure you mark the distinction between classes and instances of that class, called objects.
This distinction will hopefully become clearer as we see more examples. In the class definition, we create a kind of prototype, or specification for the construction of a objects of a certain class or type. From one class definition, we create many instances. To begin, create a new m-file with the same name as the class you want to create and start the file with the classdef keyword followed by the class name.
Properties and methods are defined and written below this line in designated blocks as shown below. We must include a special method, called the constructor , which is responsible for constructing new objects and it must have the same name as the class. The constructor can take any number of arguments specifying initial values for the properties for instance, and must return one argument, the constructed object.
Properties can optionally be assigned default values as with the minute property below. If no default is specified and no value is assigned by the constructor, they are assigned the empty matrix, [].
Below we create a class called mydate which can perform various operations to do with calendaring. The full class definition is available here , but is rather complex. We will build it up piece by piece during this chapter. We start with the constructor, called mydate, and a simple method, called rollDay. Matlab does all of the real work of creating the object, we just have to ensure that we write a constructor by the right name and perform any desired initialization, returning a declared variable.
Now that we have written the class, we can create date objects by simply calling the constructor. It is usually good practice to write a constructor so we can optionally create objects without having to specify any parameters. As we have written the mydate class, we could create a mydate object like this as well:. However, none of the properties, except for minute will be set.
They will all be equal to []. Note that if you change a class definition file, you have to type clear classes to force matlab to load the new version. Just typing clear all does not work. The properties defined above are, in java lingo, public , that is, accessible from outside the class just like fields of a struct.
We can access and assign them using dot notation. It is usually a good idea, however, to restrict direct access to properties to maintain a separation between implementation and interface. That is, we want clients to be able to use our class without having to know about the details of implementation and we will want the freedom to change how we store properties, for instance, without affecting clients already using our class.
Perhaps at a later point, for example, we want the freedom to only calculate the value of a property when the user asks for it, so called lazy evaluation.
Without a level of indirection, this would not be possible. The idea is then to provide access to properties but only through methods. We will discuss such methods, so called getters and setters shortly. Matlab offers quite a lot of control over property access. There are three levels, private , protected , and public and these apply separately to read and write access.
Private properties are only accessible from methods of the class, and public properties, the default are accessible anywhere. Protected properties are private properties that are also accessible from subclasses. We will discuss subclasses and Inheritance later in this tutorial. To mark a group of properties as say private, we modify the attributes of a property block. We saw one such property block above, however, we can create as many as we like all with different access rights so that some properties can be public and others private for example.
We specify these access rights by assigning the GetAccess and SetAccess attributes the strings 'public', 'private', or 'protected' as in the examples below. There are other property attributes we can assign although they are rarely of use with the exception of 'Constant' and perhaps 'Hidden'. We can specify that a block of properties are constant and thus cannot be changed anywhere as follows:. Hidden properties do not show up when displaying the object.
For information on additional attributes see section 6.
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