OpenModelica/C2/Functions-and-Types/English-timed

Time	Narration
00:01	Welcome to the spoken tutorial on Functions and Types.
00:06	In this tutorial, we are going to learn: how to define a function,
00:12	how to use algorithm, how to define a type.
00:17	To record this tutorial, I am using OpenModelica 1.9.2 and Ubuntu operating system version 14.04
00:27	But this process is identical in Windows, Mac OS X or FOSSEE OS.
00:35	To understand this tutorial, you need to know how to define a class in Modelica.
00:41	You need knowledge of functions in any programming language.
00:46	Pre-requisite tutorials are mentioned on our website. please go through them.
00:52	Let us discuss a function now.
00:55	function is a specialized class that can take input and return output.
01:01	It contains algorithm section.
01:04	A function cannot contain equations and it cannot be simulated.
01:10	The syntax of a function is as shown.
01:15	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.
01:36	polynomialEvaluator file is available on our website.
01:40	Please download and save all the files available in Code Files link.
01:46	To demonstrate polynomialEvaluator function, let me go to OMEdit.
01:52	OMEdit is now open in Welcome perspective.
01:56	You are only seeing a part of the OMEdit window since I have zoomed in.
02:02	I shall show you the relevant portions by shifting the window whenever necessary.
02:09	To open the files that you have downloaded, click on Open Model/Library File tool.
02:16	I have saved all the files in a folder.
02:19	Let me select them together and click on open.
02:24	If we have saved these files in different folders, you may open each one of them individually.
02:31	Note that the following classes or functions are now open in OMEdit: bouncingBallWithUserTypes , functionTester ,multipleFunctionTester, multiplePolynomialEvaluator and polynomialEvaluator.
02:51	To open polynomialEvaluator function and view it, Right-click on the icon in Libraries Browser and select View Class.
03:02	If the function doesn’t open in Text View, open it in Text View.
03:08	Name of this function is polynomialEvaluator as we have already discussed.
03:14	x is a real variable.
03:17	input is a keyword which is used to specify input variables.
03:22	Similarly, output is a keyword which is used to specify output variables.
03:28	fx is a real variable which represents f(x).
03:33	Any variable or parameter which is neither input nor output is specified using protected keyword.
03:42	a is a real parameter with a value of 1.
03:47	The values of a, b and c are as discussed in the slides already.
03:53	Please note that a, b and c are protected parameters.
03:59	Algorithm represents the beginning of algorithm section of a function.
04:05	Algorithm section may contain assignment statements only.
04:10	This sign indicates assignment.
04:14	In an assignment statement, the value of right hand side is assigned to the left hand side.
04:20	The left hand side is usually an unknown expression.
04:25	In this case, fx is an unknown variable.
04:29	The value of right hand side expression here can be calculated if the value of x is known.
04:36	x is usually passed as an input argument to the function whenever it is called.
04:43	Now let us see how to call a function using functionTester class.
04:49	functionTester icon can already be seen in Libraries Browser since I have already opened it.
04:56	To open this class, double-click on its icon.
05:01	This is an alternative way of viewing a class.
05:05	you may also right click on its icon and select View Class.
05:11	z is a real variable.
05:14	polynomialEvaluator function is called with an input argument of 10 units and it is equated to z.
05:23	The input value (variable) of polynomialEvaluator that is x takes the value of 10 units.
05:31	Now, let us simulate this class.
05:34	To simulate this class, you may right click on functionTester icon in Libraries Browser and select Simulate.
05:45	The class has now simulated.
05:47	You may also use the Simulate button in toolbar to simulate a class.
05:53	Now let me show you the Plotting perspective completely by shifting OMEdit window to the left.
06:00	Select z in the variables browser
06:04	Note that the value of z is equal to the value of f(x) at x = 10.
06:12	Now let me de-select z and delete this result.
06:18	Let me go back to Modeling perspective.
06:21	Click on polynomialEvaluator tab at the top.
06:25	Notice that polynomialEvaluator function has only one output variable.
06:31	Now let me show you how to output two or more variables using a function.
06:38	I have created a function named multiplePolynomialEvaluator which has two output variables.
06:45	Before viewing that function, let me close the tabs of PolynomialEvaluator and FunctionTester.
06:54	Since the Libraries Browser is not visible, let me shift the window to the right.
07:01	Double-click on multiplePolynomialEvaluator, multipleFunctionTester and bouncingBallWithUserTypes.
07:11	Shift the window back to its place.
07:15	Go to multiplePolynomialEvaluator tab.
07:19	This function is similar to polynomialEvaluator function except for an additional output variable.
07:27	An output variable name gx has been declared.
07:32	gx is assigned the value of a x (squared) (minus) b x (plus) c
07:38	The order in which output or input variables are declared is important.
07:45	We will understand more about this when we discuss multipleFunctionTester class.
07:51	Now, let me switch to multipleFunctionTester tab.
07:56	y and z are declared as real variables.
08:01	multiplePolynomialEvaluator function is called with an input argument of 10 units.
08:08	This means that the input variable of multiplePolynomialEvaluator takes a value of 10 units.
08:17	y and z take the values of f(x) and g(x) at x = 10 respectively.
08:26	y takes the value of output variable fx since the declaration of fx appears before the declaration of gx in the function.
08:37	Now let me simulate this class.
08:40	Click on ‘Simulate’ button. Close the pop up window.
08:46	Select y and z in the variables browser.
08:51	Note that the values of y and z are the same as f(x) and g(x) at x = 10 respectively.
09:01	Delete the result and go back to Modeling Perspective.
09:06	Now, let me interchange the order of y and z.
09:11	Delete (y,z) and type (z,y)
09:17	and save this class by pressing Ctrl+S.
09:22	Simulate this class once again. Close the pop-up window.
09:28	Select y and z in the variables browser once again.
09:33	Note that the values of y and z have been interchanged as compared to the previous case.
09:41	Let me delete this result and go back to Modeling Perspective.
09:47	Let me go back to the slides.
09:50	algorithm is Modelica syntax element to enable procedural programming.
09:56	Only assignment statements are allowed in algorithm section.
10:01	Assignment statements use the following symbol.
10:06	Data flows in assignment statements from right to left.
10:10	There are certain restrictions on functions defined in Modelica.
10:16	Use of der() in a function is invalid. Use of time variable is not allowed.
10:23	Use of when statements is not allowed in a function.
10:28	A function may not have more than one algorithm section and Models cannot be passed as arguments.
10:36	type is a specialized class to define custom data-types in Modelica.
10:42	For example, physical quantities like velocity and current can be defined as data-types.
10:50	They can be used later to declare other variables.
10:54	Attributes of Modelica data-types like unit and start can be changed accordingly.
11:01	For example, in the above case velocity is defined to be the same as real data type.
11:08	But its unit modified to meter per second (m/s).
11:12	I have created a model named bouncingBallWithUserTypes to simulate type definitions.
11:19	Let me go back to OMEdit to demonstrate this model.
11:24	Click on bouncingBallWithUserTypes tab.
11:28	This model is similar to the bouncingBall model which was discussed in previous tutorials.
11:35	Please go through the per-requisite tutorials to understand bouncingBall model.
11:41	Length is defined as Real datatype with its unit modified to meter (m) .
11:47	Similarly Velocity is defined as Real with its unit modified to meter per second (m/s) .
11:54	h represents height of the ball from surface of earth.
11:58	It is defined as length datatype.
12:02	Similarly, v represents velocity of ball.
12:05	It is declared to be of velocity datatype.
12:09	Remaining variable declarations and equations of this model are similar to bouncingBall model.
12:18	Now let me simulate this. Close the pop-up window.
12:24	In the Variables Browser, notice that h and v have their respective units associated with their data-types.
12:34	Let me select h in the variables browser.
12:38	The plot of h versus time is similar to that of bouncingBall model.
12:43	Let me de-select h.
12:46	Now, let me go back to the slides.
12:49	As an assignment, breach the restrictions on functions and observe the errors produced.
12:56	This brings us to the end of this tutorial.
12:59	Watch the video available at following link. http://spoken-tutorial.org/ What_is_a_Spoken_Tutorial It summarizes the Spoken Tutorial project.
13:05	We conduct workshops using spoken tutorials. Please contact us.
13:10	If you have questions in this spoken tutorial, please visit the website.
13:15	We coordinate coding of solved examples of popular books. Please visit the websites for more information.
13:23	We help migrate commercial simulator labs to OpenModelica.
13:29	Spoken Tutorial Project is supported by NMEICT, MHRD, Government of India.
13:36	We thank the development team of OpenModelica for their support. Thank you.

Contributors and Content Editors

Jyotisolanki, Sandhya.np14