Page 632 - ExtendSim User Guide
P. 632

606
Model Execution
Time units
As discussed in “Local time unit” on page 606, when the model uses a specific global time unit, you can change the local time unit to be anything you want.
☞ If you change the global time unit in the Simulation Setup dialog, be sure that the new time unit is appropriate for all blocks that use the default time unit. For example, if the global time unit was in hours and you change it to days, a block that used two hours will now use two days if it is set to use the default time unit.
Local time unit
You can only change the local time unit in a block if the model is using a specific global time unit, as discussed on page 605. As long as a block’s time unit is in default mode, the local time unit will be the same as the global time unit. For instance, if you change the global time unit in the Simulation Setup dialog, it will also change in every time-based block. However, as soon as you select a different time unit from the popup menu in a block, the local time unit changes from the default to that new time unit.
You can thus choose any unit of time for each time-based parameter in each block in the model. This means you can specify the parameter’s time locally as milliseconds, seconds, minutes, hours, days, weeks, months, or years, regardless of the global time unit.
Local time unit is minutes; global time is set to a different time unit
☞ In continuous and discrete event models, a local time unit applies only to its associated time- based parameter. For instance, an Item library block can have two local time units, each associ- ated with a different parameter. In discrete rate models however, the local time unit applies to the entire block. There can only be one local time unit for a discrete rate block.
If a local time unit is specified, ExtendSim will automatically convert parameters based on the local time unit’s relationship to the global time unit. If the model is using Calendar date defini- tions (see “Calendar dates”, below) that conversion will be based on the calendar. For example, the actual number of days in the month selected. If the model is not using Calendar dates, the conversion will use the non-calendar definitions entered in the Simulation Setup dialog, as dis- cussed in “Time unit conversions (non-Calendar dates)” on page 607.
Selecting a specific global time unit provides consistency when adding new blocks to the model, since every new block will initially be using the same time unit. However, in some cases you will not want to keep all parameters in default mode. Explicitly selecting a time unit (even the same unit of time as the global time unit) for each local parameter in the model is a safer choice. Then, if you subsequently decide to change the global time unit, you will not accidentally affect the simulation results.
☞ You can select a time unit from the popup that is not the default but which has the same name as the default global time unit. For instance, you can select hours from the popup, rather than hours*. You would do that if you do not want the local time unit to change based on a change in the global time unit.
Calendar dates
Sometimes it is helpful have the duration of simulation expressed in terms of a calendar-based starting and ending time. Calendar dates is a time and date format that corresponds to the cal- endar and a 24-hour clock. It is an option that you can choose in the Simulation Setup dialog, along with the Start time, End time, and Global time unit entries.
Calendar dates are not available if the global time unit is Generic, if milliseconds has been selected as the specific global time unit, or if months or years have been selected as the specific
How To


































































































   630   631   632   633   634