april 07 # 11

Discussion in 'CT4' started by MindFull, Apr 7, 2008.

  1. MindFull

    MindFull Ton up Member

    An airline has N adjacent check-in desks at a particular airport, each of which can handle any customer from that airline. Arrivals of passengers at the check-in area are assumed to follow a Poisson process with rate q. The time taken to check-in a passenger is assumed to follow an exponential distribution with mean 1/a.

    Answer: The possible states are 0 to N desks in use with no passengers queuing, and N desks in use with 0, 1, 2, ….. passengers in the queue.
    When all desks are occupied and there are M passengers in the queue denote
    the state as N:M.
    State space is:
    {0, 1, 2, …., N - 1, N : 0, N : 1, N : 2, …..}

    I understand why the trans. rate from 1 to 0 is "a" (that's the parameter for the exp func.) but the ques is why do we multiply by the number of desks that are occupied, eg. 2a, Na.

    Thanks.
     
  2. LondonStudent

    LondonStudent Member

    We multiply by the number of desks because the probability of someone leaving a desk increases the more desks that are currently taken.
     
  3. Lewin

    Lewin Member

    confused

    part iv) kolmogorov foward eqtns in component form
    The 2nd answer gives d/dt Pr(t)=a(r+1)Pr+1(t)+qPr-1(t)-(ar+q)Pr(t)
    for r+1<=N

    However,taking say r=2, we can move as follows:
    3-3-2
    3-2-2
    1-1-2
    1-2-2

    so im getting
    d/dt Pr(t)= a(r+1)Pr+1(t)+qPr-1(t)-2(ar+q)Pr(t)

    mine has a 2 before the last part while the examiners answer doesnt..........anyone explain where im going wrong?
     
  4. Hemant Rupani

    Hemant Rupani Senior Member

    I would do as (transition force in - transition force out)
    And get same result....
    \( 3aP_3(t)+qP_1(t)-(2a+q)P_2(t) \)
    I can't understand how you did?
     
    Last edited: Sep 15, 2014
  5. Lewin

    Lewin Member

    I figured out my mistake,thanks Mr Rupani
     

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