ASCEND/C2/Writing-basic-model/English

Tutorial 3: Developing a Basic model in ASCEND

Visual Cue	Narration
Open Slide number 1 Title slide	Welcome to the spoken tutorial on Developing a Basic Model in ASCEND
Open Slide 2 Learning Objectives	In this tutorial, We will learn how to Build a basic model Add methods to the basic model and Write dimensionally consistent equations
Open Slide number 3 System Requirement	Here I am using Ubuntu Linux OS v. 12.04 ASCEND v. 0.9.8
Open Slide number 4 Pre-requisites	To know more about ASCEND Please visit ascend4.org For relevant tutorials please visit our website http://spoken-tutorial.org
Open Slide number 5 Example	Let us begin the tutorial with a simple example. In this example, let us solve 3 simultaneous equations with 3 unknowns. We will use a text editor like gedit to write our model
	I already have the code for the example in a text file Let me explain the code
Open mymodel.a4c in gedit	Open the file mymodel.a4c in a text editor
Highlight the “system.a4l” line	Initially we mention the library (that is a collection of pre-defined models that we need in our model). Here we require the basic system.a4l library
Highlight the “system.a4l” line	.a4l extension denotes the ascend4 library The name of the library is written in double quotes.
Highlight the semi colon	Note that semi colon is a statement terminator in ASCEND. ASCEND considers all the statements as one sentence if semi colon is not put after each statement.
Highlight MODEL my_model	MODEL my_model begins a model with name my_model You can give any name to the model
Highlight (*variables declaration*)	In ASCEND comments are written in parenthesis enclosed with in a pair of asterik mark. Comments are not executed. They make the model easier to understand. We will now define the variables for our model.
Highlight solver_var	Any variable whose value is expected to be computed by ASCEND, must be of type solver underscore var
Highlight all the defined variables	Thus we define variable x,y,z,d and a as a solver_var The definition of the type solver_var is predefined in the system.a4l library IS underscore A is an operator in ASCEND which is used to define variable types.
Highlight all the equation sequentially	The equations to be solved are x+y+z = a*d x+y+2*z = 5 and 5*x+2*y-3*z = 0
Highlight continues	Note that we have not mentioned how to solve this given set of equations. We have also not mentioned which variables are to be specified and which are to be calculated.
Highlight END my_model	Now end this model with END my_model
Show the loaded model on ASCEND interface	Now open this model in ASCEND.
Highlight the successful execution line in the message panel	Note that ASCEND has executed the on_load method by default. This can be seen from the message in the panel below.
Highlight the values of the variables on ASCEND interface	Observe that ASCEND has given default values of 0.5 to each of the variables.
Click the solve button	Now click on the Solve icon. ASCEND displays the result.
Highlight the converged message in the panel below	This can be confirmed in the panel below. A converged message is displayed after the successful completion of the calculations.
Highlight the values of the variables y and d	Note that ASCEND squared the system automatically by keping the values of two variables y and d as default values and calculated the values for rest of the variables.
Right click on d and assign it a value 1. Fix d by selecting the fixed option. Repeat the same for x.	Now suppose we want to make x and d as our fixed variables'Bold text by assigning values to them and solve for a, y and z'. Then, right-click on d and select Properties from the drop down menu. Under Values, assign a value to d Here I am giving the value 1. Now in Solving section, select Fixed. Click on Apply and OK. Now similarly repeat the same procedure for fixing the value of x
Highlight the corresponding results	Observe that ASCEND has solved the model and you will have a new set of results. Note that the fixed variables are shown in green color and free variables, calculated by ASCEND are shown in blue color. Also note that the final results has been displayed with a tick mark and the fixed variables have been denoted by a closed lock icon. We can also specify the fixed and free variables in the code and assign values to the variables. In ASCEND the solution procedure is separate from the problem statement. Methods contain procedures to solve the model.
Open my_model in gedit	We will now explain different methods to solve our model. Open the file my_model.a4c in a text editor. We write the methods after equations.
Delete END my_model and remove asterik from METHODS and end of the code	Now remove the line END my_model. Delete the parenthesis and asterik mark in front of METHODS and at the end of the code.
Highlight the corresponding lines in the code sequentially	Under METHOD specify, we fixed variables a and d. We also assign values to the variables as a = 1 and d = 3.
	Note that to assign the values to a particular variable, we use a colon and = sign together. I will refer := (colon and equal to) sign as is equal to from here on.
Highlight the corresponding lines in the code sequentially	Under METHOD on_load, we run the METHOD specify. This is the method that describes ASCEND the action to be taken when a model is loaded.
Click on the save button	Now end the METHOD on_load and my_model and save this file.
Show the ascend interface	Now open this with ASCEND.
Select the on_load method and run the code	Now under Methods select on_load Click on Run.
Click on the solve button and highlight the asnwers	And then click on Solve icon. Observe that ASCEND has fixed the variables a and d and calculated the values for x, y and z.
Open the code file again in gedit	Now open the code for my_model.a4c again.
Carry out the required editing in the code file	Now remove the values assigned under specify.
Type as per narration	Now we will add a new METHOD called values. Type METHOD values and then type a = 1, d= 2 and END values
Type as per narration	Now under on_load type RUN values after RUN specify.
Open the file with ascend	Now save the file and open it with ASCEND.
Run the code using on_load method and press solve	Again run the Method on_load and click on Solve. You will see ASCEND has fixed variables a and d and assigned the values as mentioned under Values section in the code.
Open the required code file in gedit	Now let’s look at an interesting feature of dimensional consistency in ASCEND with the help of another model. Here we will compute the mass of a cylinder.
Type as per narration	I already have the code for this model. Let me explain the code. Open cylinder.a4c with a text editor.
Highlight the corresponding line in a sequential order	Note that, *here we require atoms.a4l library as compared to systems library, used earlier in the last model
Highlight continues	atoms is a refined version of systems library. and contains the definition of various variable types that represent different physical units
Highlight the corresponding line in a sequential order	For example, we write v is a volume m is a mass etc. Volume, mass etc. are different variable types defined in atoms.a4l This helps in ensuring that the equations written in ASCEND models are dimensionally consistent.
Scroll down the code	After this we write equations and methods as explained earlier.
Highlight the corresponding line in a sequential order	Note that, while specifying values for these variable types, we need to mention the corresponding physical units in curly brackets.. Here we write V = 100 cm cube and p = 100 kg per metre cube. Note that v is in CGS units while p is in SI units. The user doesn't have to worry about the units as ASCEND itself performs the unit conversion.
Open the file in ASCEND and run and solve it using the on_load method	Now open this file in ASCEND. Now once again run the on_load Method and solve the problem.
Highlight the answers	Observe that ASCEND has converted the values of volume into SI units and then calculated the mass in SI units Note that ASCEND, by default, uses SI units until specified otherwise.
Open Slide number 5: Summary	Now let us summarize. In this tutorial, We have learnt how to Build a basic model Add methods to the basic model and Write dimensionally consistent equations
Open Slide number 6: Assignment	Do the following assignment Edit the model cylinder in a text editor and make it dimensionally inconsistent For example, write m is a distance instead of mass Now run this dimensionally inconsistent model in ASCEND and observe the output Add more variables and equations to the model cylinder.a4c and solve it in ASCEND
Open Slide number 7 About the Spoken Tutorial Project	Information on the spoken tutorial project is available on our website spoken-tutorial.org
Open Slide number 8 Spoken Tutorial Workshops	Details on Workshops based on spoken tutorials is also available on the website
Open Slide number 9 Acknowledgements	Spoken tutorial project is funded by NMEICT,MHRD
Open Slide number 10 Thank You	This is Priya Bagde from IIT Bombay signing off Thank You for joining

Contributors and Content Editors

Nancyvarkey, Tarung