Page 46 - ExtendSim User Guide
P. 46

20 Running a Model
Making changes to the model
You can change a model by adding or removing blocks or by changing parameter values in a block’s dialog.
Adding and removing blocks
If you have some processes running in parallel (such as the two water sources in the Reservoir model), you can easily test the results of adding additional parallel processes or removing existing ones.
You will learn how to add blocks in “Building a Model” on page 23.
To remove a block, click it to select it, then choose Edit > Clear Blocks or use the Delete or Backspace key. Note that deleting a block removes its associated connections as well.
Changing dialog parameters
You can change a dialog value by clicking in a parameter field while the model is running. When you do this, ExtendSim pauses the simulation. To continue the simulation, select Run > Resume or click the Pause/Resume tool in the toolbar. Note that when you make changes to a dialog and then save the model, the changes are saved with it.
On page 587 you will see how to vary a dialog value manually using Controls, such as Sliders, and on page 650 how to use scenario analysis to automatically explore various options. For simplicity, parameters in the following blocks are entered in the dialog as static values that do not change based on model conditions. To see how easy it is to change dialog parameters and see the impact on results, try some of the following suggested changes.
Lookup Table block (Rainfall)
The Lookup Table block provides a time- varying value (in this case, the amount of rainfall each month) for the simulation.
This block looks at the current simulation time, compares it to the time values in the column labeled Months, and outputs the corresponding Rain (inches) value.
Right now, the Lookup Table block shows that 2.6 inches of water are fed into the reservoir at time 0, the beginning of the run, 4.4 units at the beginning of the next month, and so on.
Change the first value in the Rain column from 2.6 to a high number, such as 90, then run the simulation again to see the impact on the results. (To change the number, type 90 in place of 2.6. Then click somewhere outside of the cell, or OK, to save the change.)
Lookup Table block dialog
Tutorial


































































































   44   45   46   47   48