Page 323 - ExtendSim User Guide

P. 323

```
Gathering statistics
The Statistics block (Value library) accumulates data and calculates statistics for a particular type of block using a specified statistical method. In addition to the block number, block name, and the time the information was observed, this block displays metrics that are specific to the block type, such as utilization or average wait time for activity-type blocks or the mean, vari- ance, and standard deviation of all the Mean & Variance blocks in the model.
The Queue Statistics model, located in the folder \Examples\Discrete Event\Statistics, uses the Statistics block to gather information about queues.
Since the Statistics block is used to gather information in continuous, discrete event, and dis- crete rate models, it is discussed fully in “Statistics” on page 642.
Clearing statistics
At the start of a simulation run the queues are often empty and operations have nothing to pro- cess. After the model has been running for a while, it gets to the point where it is functioning more like the real system at normal operating levels. The interval from when the model starts to when it is functioning in a steady or normal state is called the warm-up period.
The Clear Statistics block (Value library) is used to reset statistical accumulators for the blocks specified in its dialog, eliminating the statistical bias of the warm-up period. For more informa- tion about this block, see “Clear Statistics” on page 644.
Clearing Statistics model
Clearing Statistics model
In the Clearing Statistics model, statistics are cleared after 40 seconds, removing the warm-up period for the model. This is seen by the utilization of 1 for Activity B when the model is run. Unchecking the Clear activity statistics checkbox on the model worksheet causes the utiliza- tion of Activity B to approach, but never actually reach, 1. This is due to the effect of the initial idleness of the Activity B block at the start of the simulation run.
Using the History block to get item information
When building a model, it is important to start small, verify that the section you have built is working as expected, then enhance that model section. The History block is particularly useful for verifying model data because it provides important information about each item as the sim- ulation runs.
There are two ways to add a History block to a model:
Statistics and Model Metrics 297
Gathering statistics
Discrete Event
```