HELP - Normal vs Exponential Distribution Discrete Event Model

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extendnovice
Posts: 7
Joined: Sun Jul 21, 2019 4:45 pm
First Name: Paul
Last Name: Davis

HELP - Normal vs Exponential Distribution Discrete Event Model

Post by extendnovice » Fri Aug 16, 2019 9:29 am

I am working on the car wash discrete event model in ExtendSim. When I change the parameters between a normal and exponential distribution my results change and I do not understand why.

I think it has something to do with the mean of each distribution? I'm kind of lost.

ceciledamiron
Posts: 55
Joined: Wed Jul 02, 2008 12:10 pm
First Name: Cecile
Last Name: Damiron

Re: HELP - Normal vs Exponential Distribution Discrete Event Model

Post by ceciledamiron » Fri Aug 16, 2019 12:02 pm

Hello Paul,

First of all if in order to determine the delayTime attribute value you chose an exponential distribution it is most likely a bad choice. As described in the Random number block help about the exponential distribution: "Use it to represent the length of a telephone conversation, the expected lives of electronic components, the time between failures for equipment, or any other situation where the events are completely independent of each other. It is generally not appropriate for modeling delay or processing times."

Second of all, when you change the distribution, the draw of random number changes and the delay for each car to be washed will be different. It is the definition of a stochastic model. To help you visualize what is happening you should add a history block after the Equation I block. You will then have a log of each car and you will be able to visualize the value of the delayTime attribute for each car.
You can add a History block by hovering your mouse on the output Item connector of the Equation I block, right click and select "Add" in the section "Options for History"

Cecile

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