In this lecture we are going to look at tools present on the system analysis toolbar in Vensim. These are tools that help analyze the behaviour of the model and the variables included. 1
The lecture will first explain the notion of workbench variable. Then it will give an overview of System analysis toolbar and show examples of using the tools located on this toolbar. 2
Workbench variable is any variable that is selected at a particular moment. Usually when working with the analysis toolbar the Lock sketch tool is selected on the scetch toolbar. At this point we usually want to analyze the results from the simulation and not to change some part of the sketch. Hence, the selected variable at this point is the one for wich we want to get more information or inspect its behaviour over time. Each tool from the analysis toolbar will give us more information about the workbench variable. The name of this variable appears on the title bar of the Vensim Window next to the name of the model. In case when no model is opened the FINAL TIME variable is displayed as a benchmark variable. 3
The analysis toolbar is located on the left side of the Vensim Window. It is divided into two parts. The upper part contains tools for structural analysis, or tools that help with analyzing the structure of the model, the cause effect sequences, the feedback loops. The lower part contains tools for analysis of the datasets obtained during simulation. 4
The tools for structural analysisareare the following: Causes tree tool that gives a separate window presenting the causes of the workbench variable. It shows the variables that have influence over the changes of the workbench variable Uses tree tool opens a window presenting which variable make use of (are influenced by) the workbench variable Loop tool shows the list of feedback loops passing through the workbench variable Document tool shows the equations, the values, and the units of measurement for the workbench variable Document all tool differs from the Document tool in being more comprehensive. It gives information about all variables on the sketch. 5
The tools for dataset analysisareare the following: Causes strip graph shows BOTGs for the benchmark variable and two other variables that are causing effects on this variable. The graph tool displays the BOTG of the workbench variable. The horizontal table tool generates a table with the data set for the workbench variable obtained during simulation. The data are presented horizontally. The vertical table presents the samedataset asthe horizontal one. The only difference is that the data are presented vertically. Runs compare tool compares two or more data sets if these data sets are loaded. 6
On the next slides examples with all of these tools are presented. This slide shows the causes and uses tree for the population variable in a simple population model. 7
The stock variable Population is a benchmark varaiable and it is a part of the two feedback loops present in the model. The list of the variables in each loop is presented in a separate window using Loops tool. The separate windows can be printed or saved as a separate text file. 8
This slide shows windows that pop up with the Document and Document all tool in the simple population model. 9
The graph of the population and the causes strip graph (population, births and deaths) are presented here. 10
The dataset obtained for population during the simulation is presented as a horizontal and as a vertical table. 11
Here the two different runsallcalled Current and Current1. The pop up window provoked with Compare runs tool shows the differences inthe two runs. Here the date rate has been changed. 12