Almost all of your model building work is done from this VORSIM Model Builder control sheet. The end goal is a free-standing model workbook accessed by the Model button on a control screen.
VORSIM is a button (or icon) driven program to help you build a model in the Microsoft Excel spreadsheet. The code is written in VBA (Visual Basic for Applications) that is the “macro” language for Excel. Beside the normal commands of Basic, VBA has added commands which control most Excel operations. Furthermore, VBA Excel commands can be created by recording Excel operations done manually. In short, VBA includes Basic commands plus Excel spreadsheet commands, giving VBA considerable power in the spreadsheet environment. To facilitate the model building capability of VBA, file and variable naming conventions are imposed which uses a spreadsheet structure to contain model files, variable names, and equation terms. A model consists of equations calculating variable values and includes a way of closing markets by changing variables such as prices. Equations are built as a set of terms which involve a variable and a math operation. An example using Excel math notation might be Y=constant*var1^.4*var2^-.1. Three terms would be “constant”, *var1^.4, and *var2^-.1. In a model, variable values are kept in spreadsheet cells. Variable names are a concatenation of a sheet name, a variable type name, and a set of categories. Look at the DEMO model and the User Guide to learn more. Basically, model formats are user designed but compatible with the spreadsheet structure. |