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Pareto Distribution

  • 17-11-2009 12:21am
    #1
    TommyGunne
    Closed Accounts Posts: 2,771 ✭✭✭


    OK, so this is obv a homework question, and so I don't want people to be providing me with code/doing anything for me. My question is about the seed that is mentioned. I just can't figure out what this refers to. The mean and the variance given translate back to an alpha of 3 and a lambda of 4000 for this distribution (fx(x) = (al^a)/((l+x)^(a-1))), but I simply have no idea as to what the seed refers to. Perhaps a shift to the right? That would mean that the question was phrased oddly though....

    1) Generate a random sample of size 120 from a Pareto distribution with mean 2000 and
    variance 12,000,000 using as a seed your student number.


Comments

  • #2
    LeixlipRed
    Closed Accounts Posts: 6,081 ✭✭✭LeixlipRed


    I remember reading a paper once were Pareto distributions were used in conjuction with peer to peer file sharing networks. Unfotunately I know nothing more but that could be were the "seed" is involved. A quick google leads me to nothing!


  • #3
    TommyGunne
    Closed Accounts Posts: 2,771 ✭✭✭TommyGunne


    Yeah prolonged googling of it for me has turned up nothing either. Perhaps its to do with the random number generation? I know I've heard of seeds wrt rngs before, but have no idea about it.

    I'm using R, and the function I'm using is:

    rpareto <- lambda*(((runif(n))^(-1/alpha))-1)

    The only thing googling has turned up has something to do with random number generation, but I have no idea what to do with it.


  • #4
    LeixlipRed
    Closed Accounts Posts: 6,081 ✭✭✭LeixlipRed


    Hmmm, you might get more luck in another forum possibly? Can you not just ask whoever set the assignment?


  • #5
    TommyGunne
    Closed Accounts Posts: 2,771 ✭✭✭TommyGunne


    LeixlipRed wrote: »
    Hmmm, you might get more luck in another forum possibly? Can you not just ask whoever set the assignment?

    Both good ideas. TY.


  • #6
    Thomas_S_Hunterson
    Closed Accounts Posts: 6,151 ✭✭✭Thomas_S_Hunterson


    The seed in this case is just the seed for the (pseudo)random number generator.

    Use following to set the RNG seed in R: 
    set.seed(123456789)


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  • #7
    Fremen
    Registered Users, Registered Users 2 Posts: 2,481 ✭✭✭Fremen


    Yeah, Sean K has the right idea. Your lecturer's asking you to set the seed like that so he can reproduce your results and check that they're correct. Starting from the same seed, a RNG will always produce the same results.


  • #8
    TommyGunne
    Closed Accounts Posts: 2,771 ✭✭✭TommyGunne


    Cool. That explains it perfectly!

    Thanks for the help.


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