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To: cs551@merlot.usc.edu
Subject: Re: CS551: statistics calculation
Date: Fri, 08 Sep 2006 14:48:57 -0700
From: william@bourbon.usc.edu
Someone wrote:
> Since the poisson distribution only corresponds to only inter-arrival
> times and service times, I'm not sure how to calculate the following
> statistics:
> Let me know if the following assumptions are correct. And how to
> calculate 3 & 4.
> 1. customer drop probability = (number of
> customers dropped / total number of customers) ?
This is correct.
> 2. average number of customers in Q1 = (number of
> customers/size of Q1) ?
This is not correct. If 50% of the time Q1 is empty,
30% of the time Q1 has 1 customer, and 20% of the time
Q1 has 2 customers, then the average number of customers
in Q1 is:
0.5 * 0 + 0.3 * 1 + 0.2 * 2 = 0.7
> 3. average number of customers at S1 =
> 4. average number of customers at S2 =
If 60% of the time S1 is empty and 40% of the time
S1 has 1 customer, then the average number of customers
at S1 is:
0.6 * 0 + 0.4 * 1 = 0.4
This is the same as saying the probability that S1
is busy or the utilization of S1.
--
Bill Cheng // bill.cheng@usc.edu