View source for OpenModelica/C2/Functions-and-Types/English

{| border=1
||'''Visual Cue'''
||'''Narration'''
|-
||'''Slide Number 1'''

'''Title Slide'''
|| Welcome to the spoken tutorial on '''Functions and Types'''.

|-
|| Slide:

'''Learning Objectives'''
|| In this tutorial, we are going to learn:

* How to define a '''function'''.

* How to use '''algorithm'''.

* How to define a '''type'''.

|-
|| Slide:

'''System Requirements'''
|| To record this tutorial, I am using

* '''OpenModelica 1.9.2''' and '''Ubuntu operating system version 14.04''' 

* But, this process is identical in '''Windows''', '''Mac OS X''' or '''FOSSEE OS'''.

|-
|| Slide:

'''Pre-requisites'''
||To understand this tutorial You need to know how to define a '''class''' in '''Modelica'''.

* You need knowledge of '''functions''' in any programming language.

* Pre-requisite tutorials are mentioned on our website. 

* please go through them.

|-
|| Slide:

'''function'''
|| Let us discuss a '''function''' now.

'''function''' is a specialized class that can take input and return output.

It contains '''algorithm''' section.

A '''function''' cannot contain equations and it cannot be simulated.

|-
|| Slide:

'''Syntax of function'''
|| The syntax of a '''function''' is as shown.

|-
|| Slide:

'''Problem Statement'''
|| Now let us write a '''function''' named '''polynomialEvaluator''' which

* takes '''x''' as input and

* returns '''f(x) = a x (squared) (plus) b x (plus) c''' where '''a=1, b=2''' and '''c=1''' as output.
'''
|-
|| /* OMEdit */
|| '''polynomialEvaluator''' file is available on our website.

Please download and save all the files available in '''Code Files''' link.

To demonstrate '''polynomialEvaluator''' function, let me go to '''OMEdit'''.

'''OMEdit''' is now open in '''Welcome''' perspective.

You are only seeing a part of the '''OMEdit''' window since I have zoomed in. 

I shall show you the relevant portions by shifting the window whenever necessary.

|-
|| '''‘Open Model/Library file’''' tool
|| To open the files that you have downloaded, click on '''Open Model/Library File''' tool.

I have saved all the files in a folder. 

Let me select them together and click on '''open'''. 

If we have saved these files in different folders, you may open each one of them individually.

|-
|| 
|| Note that the following '''classes''' or '''functions''' are now open in '''OMEdit''': 

* '''bouncingBallWithUserTypes'''

* '''functionTester'''

* '''multipleFunctionTester'''

* '''multiplePolynomialEvaluator''' and

* '''polynomialEvaluator'''.

|-
|| Point to '''Text View''' icon.
|| To open '''polynomialEvaluator''' function and view it, Right-click on the icon in '''Libraries Browser''' and select '''View Class'''. 

If the function doesn’t open in '''Text View''', open it in '''Text View'''.

|-
|| /* polynomialEvaluator */

'''function polynomialEvaluator'''
|| Name of this '''function''' is '''polynomialEvaluator''' as we have already discussed.

|-
|| input '''Real x;'''
|| '''x''' is a '''real''' variable. 

|-
|| '''input''' Real x;
|| '''input''' is a keyword which is used to specify '''input''' variables.

|-
|| '''output''' Real fx;
|| Similarly, '''output''' is a keyword which is used to specify '''output''' variables.

'''fx''' is a '''real''' variable which represents '''f(x)'''. 

|-
|| '''protected Real a = 1''';
|| Any variable or parameter which is neither '''input''' nor '''output''' is specified using '''protected''' keyword. 

|-
|| '''protected parameter Real a = 1;'''
|| '''a''' is a '''real''' parameter with a value of '''1'''.

|-
|| '''protected parameter Real b = 2;'''

'''protected parameter Real c = 1;'''
|| The values of '''a''', '''b''' and '''c''' are as discussed in the slides already.

|-
|| '''algorithm'''.
|| Please note that '''a''', '''b''' and '''c''' are '''protected''' parameters.

'''Algorithm''' represents the beginning of '''algorithm''' section of a '''function'''.

'''Algorithm''' section may contain '''assignment''' statements only.

|-
||''' fx := a*x^2 + b*x + c''';
|| This sign indicates '''assignment'''. 

|-
|| '''fx := a*x^2 + b*x + c''';
|| In an '''assignment''' statement the value of right hand side is assigned to the left hand side.

|-
|| '''fx := a*x^2 + b*x + c''';
|| The left hand side is usually an unknown expression. 

In this case '''fx''' is an unknown variable. 

|-
|| '''fx := a*x^2 + b*x + c'''<nowiki>;</nowiki>
|| The value of right hand side expression here can be calculated if the value of '''x''' is known.


|-
|| '''fx := a*x^2 + b*x + c'''<nowiki>;</nowiki>
|| '''x''' is usually passed as an '''input''' argument to the '''function''' whenever it is called.

|-
|| 
|| Now let us see how to call a '''function''' using '''functionTester''' class.

'''functionTester''' icon can already be seen in '''Libraries Browser''' since I have already opened it.

|-
|| Right-click on '''functionTester''' and select '''View Class'''
|| To open this '''class''', double-click on its icon.

This is an alternative way of viewing a '''class'''. 

you may also right click on its icon and select '''View Class'''.

|-
|| '''Real z;'''
|| '''z''' is a '''real''' variable.

|-
|| '''z = polynomialEvaluator(10);'''
|| '''polynomialEvaluator''' function is called with an '''input''' argument of '''10''' units and it is equated to '''z'''.

|-
|| '''z = polynomialEvaluator(10)'''<nowiki>;</nowiki>
|| The '''input''' value (variable) of '''polynomialEvaluator''' that is '''x''' takes the value of '''10''' units.

|-
|| Click on '''Simulate''' button.
|| Now let us simulate this '''class'''.

To simulate this '''class''' you may right click on '''functionTester''' icon in '''Libraries Browser''' and select '''Simulate'''. 

The class has now simulated.

You may also use the '''Simulate''' button in toolbar to simulate a '''class'''.

|-
|| /* Plotting perspective */

Click on '''z''' in the '''variables browser'''
|| Now let me show you the '''Plotting perspective''' completely by shifting '''OMEdit''' window to the left.

Select '''z''' in the '''variables browser'''

Note that the value of '''z''' is equal to the value of '''f(x)''' at '''x = 10'''. 

Now let me de-select '''z''' and delete this result.

|-
|| Let me go back to '''Modeling perspective'''.
|| Let me go back to '''Modeling perspective'''.

|-
|| Point to '''polynomialEvaluator'''
||Click on '''polynomialEvaluator''' tab at the top.

Notice that '''polynomialEvaluator''' function has only one '''output''' variable.

Now let me show you how to '''output''' two or more variables using a '''function'''. 

I have created a '''function''' named '''multiplePolynomialEvaluator''' which has two '''output''' variables.

Before viewing that '''function''' let me close the tabs of '''PolynomialEvaluator''' and '''FunctionTester'''.

Since the '''Libraries Browser''' is not visible, let me shift the window to the right.
|-
|| Double-click '''multiplePolynomialEvaluator'''
|| Double-click on '''multiplePolynomialEvaluator''', '''multipleFunctionTester''' and '''bouncingBallWithUserTypes'''.

Shift the window back to its place.

Go to '''multiplePolynomialEvaluator''' tab.

This '''function''' is similar to '''polynomialEvaluator''' function except for an additional '''output''' variable.

|-
|| '''output Real gx;'''
|| An '''output''' variable name '''gx''' has been declared.

|-
|| '''gx := a*x^2 - b*x + c;''' 
|| '''gx''' is assigned the value of '''a x (squared) (minus) b x (plus) c'''

The order in which '''output''' or '''input''' variables are declared is important.

We will understand more about this when we discuss '''multipleFunctionTester''' class.

|-
|| Click on '''multipleFunctionTester''' tab 
|| Now let me switch to '''multipleFunctionTester''' tab.

|-
|| /* multipleFunctionTester */

'''Real y;'''

'''Real z;'''
|| '''y''' and '''z''' are declared as '''real''' variables.

|-
|| '''(y,z) = multiplePolynomialEvaluator(10)'''<nowiki>; </nowiki>
|| '''multiplePolynomialEvaluator''' function is called with an '''input''' argument of '''10''' units.

This means that the '''input''' variable of '''multiplePolynomialEvaluator''' takes a value of '''10''' units.

|-
|| ('''y,z''') = '''multiplePolynomialEvaluator(10)'''; 

|| '''y''' and '''z''' take the values of '''f(x)''' and '''g(x)''' at '''x = 10''' respectively.

'''y''' takes the value of '''output''' variable '''fx''' since the declaration of '''fx''' appears  before the declaration of '''gx''' in the '''function'''.

Now let me simulate this '''class'''.

|-
|| Click on '''Simulate''' button.
|| Click on '''‘Simulate’''' button.

Close the pop up window.

|-
|| /* Plotting perspective */

Select '''y''' and '''z''' in the '''variables browser'''
|| Select '''‘y''' and '''z''' in the '''variables browser'''.


Note that the values of '''y''' and '''z''' are the same as '''f(x)''' and '''g(x)''' at '''x = 10''' respectively.

|-
|| Delete the result and go back to '''Modeling Perspective'''.
|| Delete the result and go back to '''Modeling Perspective'''.

|-
|| /* multipleFunctionTester */

'''(z,y) = multiplePolynomialEvaluator(10)''';

|| Now, let me interchange the order of '''y''' and '''z'''.


Delete '''(y,z)''' and  type '''(z,y)'''. 


and save this class by pressing '''Ctrl+S'''.

Simulate this '''class''' once again.

Close the pop up window.

|-
|| /* Plotting perspective */

Select '''y''' and '''z''' once again in the '''variables browser'''
|| Select '''y''' and  '''z''' in the '''variables browser''' once again.


Note that the values of '''y''' and '''z''' have been interchanged as compared to the previous case.

Let me delete this result and go back to '''Modeling Perspective'''.

|-
|| 
|| Let me go back to the slides.

|-
|| Slide:

'''algorithm'''
|| '''algorithm''' is '''Modelica syntax element''' to enable procedural programming.

Only '''assignment''' statements are allowed in '''algorithm''' section.

'''Assignment''' statements use the following symbol.

Data flows in '''assignment''' statements from right to left.

|-
|| Slide:

'''Restrictions on functions'''.
|| There are certain restrictions on functions defined in '''Modelica'''.

Use of '''der()''' in a function is invalid.

Use of  '''time''' variable is not allowed.

Use of '''when''' statements is not allowed in a function.

A '''function''' may not have more than one '''algorithm''' section and

'''Models''' cannot be passed as '''arguments'''.

|-
|| Slide:

'''type'''
|| '''type''' is a specialized class to define custom '''data-types''' in '''Modelica'''.


For example, physical quantities like '''velocity''' and '''current''' can be defined as '''data-types'''.

They can be used later to declare other variables.

'''Attributes''' of Modelica data-types like '''unit''', and '''start''' can be changed accordingly.

For example, in the above case '''velocity''' is defined to be the same as '''real data type'''.

But its unit modified to '''m/s'''.

I have created a '''model''' named '''bouncingBallWithUserTypes''' to simulate type definitions.

|-
|| 
|| Let me go back to '''OMEdit''' to demonstrate this '''model'''.

|-
|| /* bouncingBallWithUserTypes */
|| Click on '''bouncingBallWithUserTypes''' tab.

|-
|| 
|| This '''model''' is similar to the '''bouncingBall''' model which was discussed in previous tutorials.

Please go through to the per-requisite tutorials to understand '''bouncingBall''' model.

|-
|| '''type Length = Real(unit="m");'''
|| '''Length''' is defined as '''Real''' datatype. Its unit is modified to '''m'''.

|-
|| '''type Velocity = Real(unit="m/s");'''
|| Similarly '''Velocity''' is defined as '''Real'''. 

Its unit is modified to '''m/s'''

|-
|| '''Length h;'''
|| '''h''' represents height of the ball from surface of earth.

It is defined as '''length datatype'''.

|-
|| '''Velocity v;''' 
|| Similarly '''v''' represents velocity of ball.

It is declared to be of '''velocity datatype'''.

|-
|| 
|| Remaining variable declarations and equations of this '''model''' are similar to '''bouncingBall''' model.

Now let me '''simulate''' this.

Close the pop up window.

|-
|| /* Plotting perspective */
|| In the '''Variables Browser''' notice that '''h''' and '''v''' have their respective units associated with their data-types.

Let me select '''h''' in the '''variables browser'''.


The plot of '''h''' versus '''time''' is similar to that of '''bouncingBall''' model.

Let me de-select '''h'''.

|-
|| 
|| Now let me go back to the slides.

|-
|| Slide:

'''Assignment'''.
|| As an assignment breach the restrictions on functions and observe the errors produced.

|-
|| 
|| This brings us to the end of this tutorial.

|-
|| Slide:

About the '''Spoken Tutorial project'''
|| Watch the video available at following link.

'''http://spoken-tutorial.org/ http://spoken-tutorial.org] /What\_is\_a\_Spoken\_Tutorial'''

It summarises the '''Spoken Tutorial project'''

|-
|| Slide:

'''Spoken Tutorial''' Workshops
|| We conducts workshops using spoken tutorials

Please contact us.

|-
|| Slide:

'''Forum to answer questions'''
|| If you have questions in this spoken tutorial, please visit the website.

|-
|| Slide:

'''Textbook Companion Project'''
|| We coordinate coding of solved examples of popular books.

Please visit the websites for more information.

|-
|| Slide:

'''Lab Migration Project'''
|| We help migrate commercial simulator labs to '''OpenModelica'''. 

|-
|| Slide:

'''Acknowledgements'''
|| '''Spoken Tutorial Project''' is supported by '''NMEICT, MHRD''', Government of India.

|-
|| Slide:

'''Thanks'''
|| We thank the development team of '''OpenModelica''' for their support.

Thank you.