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Work out the variance of the gamma

  1. Aug 29, 2009 #1
    Hi, I'm trying to work out the variance of the gamma(I'm up the the part where you multiply [tex] x^2[/tex] by the function), but i don't know how to work out what

    [tex]\gamma(\alpha + 2) [/tex] equals to

    i know im supposed to use the fact that [tex] \gamma(\alpha + 1) = \alpha \gamma(\alpha) [/tex]

    but i dont understand what to do, please help
     
  2. jcsd
  3. Aug 29, 2009 #2

    HallsofIvy

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    Re: gamma

    It's not clear whether you are talking about the gamma probability distribution or the gamma function. The gamma function has the property that [itex]\Gamma(\alpha+1)= \alpha\Gamma(\alpha)[/itex] but is normally represented by the capital [itex]\Gamma[/itex], not [itex]\gamma[/itex].

    In any case, [itex]\Gamma(\alpha+ 2)= \Gamma(\alpha+1+ 1)[/itex][itex]= (\alpha+1)\Gamma(\alpha+1)= (\alpha+ 1)\alpha\Gamma(\alpha)[/itex].
     
  4. Aug 29, 2009 #3
    Re: gamma

    I'm not sure either, but I have to guess its the probability distribution.
     
  5. Aug 29, 2009 #4
    Re: gamma

    yupp i actually meant [tex]\Gamma[/tex] sorry about that. but thanks for the help
     
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