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Proving asymptotics to sequences

  1. Mar 21, 2007 #1

    CRGreathouse

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    Suppose I have a sequence

    [tex]a_0 = 1[/tex]

    [tex]a_n = \sum_{k=1}^n f(k)\cdot a_{n-k}[/tex]

    where f(n) is a known function (in binomial coefficients, powers, and the like).

    In general, how would I go about proving that [itex]a_n\sim g(n)[/itex]? I'm working on more closely estimating the function by calculating its value for large n, along with first and second differences. (Suggestions on better methods are welcome, though I think I'm nearly there -- the second differences look suspiciously hyperbolic.)

    Any help would be appreciated.
     
  2. jcsd
  3. Apr 18, 2007 #2

    tpm

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    umm..if we had the sequence :

    [tex]a_n +b_n = \sum_{k=1}^n f(k)\cdot a_{n-k}[/tex]

    replace the sum by an integral so:

    [tex]a(n)+b(n) = \int_{k=1}^n dkf(k)a(n-k) [/tex]

    if you obtain A(s) F(s) and B(s) as the Laplace transform of a(n) b(n) and f(k)

    [tex]A(s)+B(s)=F(s)A(s) [/tex] (using the properties of "convolution" )

    invertng you could get an asymptotic expression for a(n)
     
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