First we need to make a subscript range to describe the tasks.
| Ø | Click on the Subscript Control button on the Toolbar. |
| Ø | Click on the New… button, in the dialog box type the name task then press Enter. |
The Equation Editor opens to display the incomplete equation for task.
| Ø | Fill in the three tasks, as below, then click on the OK button. |
| Ø | Select the Equations tool and open the Equation Editor on task size. |
| Ø | Type in the numbers 180, 250, 500 |
| Ø | Click on the top edit box to the right of the name task size. Now click on the Subscripts tab and click on task (the only entry in the list). Vensim will add the square brackets [ ]. Your equation should read: |
Units: Drawing
| Ø | Continue entering the other equations. |
You will need to alternate between the Variables and Subscripts tabs. You will notice that once you have added a subscript to a variable when you click on its name in the Variable tab it will be placed in the equation with its subscript. Thus, for each variable, you only need to add the subscript once when you write the equations. Enter the equations as shown below.
| Work To Do[task] = INTEG( |
| - work accomplishment[task], |
Units: Drawing
| Ø | Check the Supplementary check box for Work To Do. |
| work accomplishment[task], |
Units: Drawing
work accomplishment[task]=
IF THEN ELSE(task is active[task],max work accomplishment[task],0)
Units: Drawing/Month
The equation for work accomplishment uses the logical IF THEN ELSE function, getting work done for each task at the maximum work accomplishment as long as that task is active.
| max work accomplishment[task]= |
Units: Drawing/Month
The four remaining variables describe the relationships of the tasks to each other. If a task has no prerequisite tasks, then it may start immediately. If a task has prerequisites, those prerequisites must finish before the task can start.
