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Here you see the
spreadsheet values for variables in the model DEMO in the base year of
1996. Cell colors mark how the
value in the cell is generated: white – exogenous data, yellow – equation
generated, green – variables changed by solver to obtain a solution, red
– target variables driven to zero by the solver, blue – one overall
target value driven to zero by the solver, light yellow – empty
spreadsheet cells. These cell
colors carry over into solutions that are saved. |
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A VORSIM model consists of up to three Excel workbooks. The DEMO model workbook is shown above but for a time series model, there also are workbooks containing exogenous data for simulation and historical data for lagged variables. In a model, color coded cells mark different types of variables. Yellow cells contain variables which are explained by model. A blue cell holds the formula targeted for zero by the solver. The DEMO model is solved by calling in new exogenous data (white cells) every time period and solving (with the Excel Solver) the {Model} sheet until the formulas in the red cells are driven to zero by changes in numbers in the green cells. In DEMO, three prices (green) drive three market equilibrium equations (red) to zero. Control buttons on the Model sheet help the user change exogenous variables, start simulation programs and save solutions with a user chosen name. The model sheet contains the time of its creation. Model sheets in the DEMO model workbook are: {1}, {2} – Sheets containing lagged data for simulation of the model DEMO. {Model} – The model sheet with yellow cells containing equations, white cells containing exogenous data, green cells containing control variables that are changed to reach a solution, and red cells containing equations targeted for solution by the Excel Solver. The number of control variables must equal the number of target cells. The blue cell holds a formula to be driven to zero by the solver. {Solver parameters} – (Not shown) Convergence tolerances, iteration limits, etc. for the Solver. This sheet is deleted when the model has been configured for solution and the Solver has been installed. {Current solution status} – A sheet containing tables of beginning and final solution target and control variables for each time period for the current solution. This information helps verify a satisfactory solution or diagnose solution problems if a model does not converge to zero equilibrium values for target cells. A solution is saved as a named workbook using the formats on the model sheet. The solution workbook has a series of sheets (one sheet for each time period). The time of solution generation is entered automatically when the solution is saved. Textboxes containing explanations of the model can be added to the model workbook for documentation purposes. A model is structured the same way in VORSIM 15 as in previous VORSIM versions (such as version 14). The only difference is that the improved Excel 2013 solver is used rather than the one commonly used in previous VORSIM versions. |