Distribution

duncan smith buzzard at urubu.freeserve.co.uk
Tue Mar 20 21:19:28 CET 2012


On 20/03/12 04:31, prince.pangeni wrote:
> Hi all,
>     I am doing a simulation project using Python. In my project, I want
> to use some short of distribution to generate requests to a server.
> The request should have two distributions. One for request arrival
> rate (should be poisson) and another for request mix (i.e. out of the
> total requests defined in request arrival rate, how many requests are
> of which type).
>     Example: Suppose the request rate is - 90 req/sec (generated using
> poisson distribution) at time t and we have 3 types of requests (i.e.
> r1, r2, r2). The request mix distribution output should be similar to:
> {r1 : 50 , r2 : 30 , r3 : 10} (i.e. out of 90 requests - 50 are of r1
> type, 30 are of r2 type and 10 are of r3 type).
>     As I an new to python distribution module, I am not getting how to
> code this situation. Please help me out for the same.
>
>    Thanks in advance
>
> Prince

Robert has given you a very good answer. The easiest way is to generate 
interarrival times using an exponential distribution, then for each 
event select the type from a categorical probability mass function. 
Perhaps the easiest and most efficient approach for the latter using 
your 'mix distribution' above is to create a list containing 5 instances 
of r1, 3 of r2 and 1 of r3. Then select the type by generating a random 
index into the list. It is not an ideal solution generally, but good 
when the parameters do not change and the required list is small.

Duncan



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