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Old Nov28-09, 07:00 PM                  #1
Jarle

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growth of a function

Does there exist a continuous function which outgrows polynomial growth, but not exponential growth?

I.e. does a there exist a continuous function f such that LaTeX Code: \\frac{x^n}{f(x)} \\to 0 and LaTeX Code: \\frac{f(x)}{a^x} \\to 0 for all positive real n and a?
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Old Nov28-09, 08:33 PM                  #2
hamster143

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Re: growth of a function

Yes. Look at it this way: you take logs of the polynomial and the exponential, you get LaTeX Code: g_1(x) = C_1 \\ln x and LaTeX Code: g_2(x) = C_2 x . Can you find a function that grows faster than g_1 and slower than g_2 for all C? Clearly you can, because ln grows extremely slowly.
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Old Nov28-09, 10:09 PM                  #3
Jarle

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Re: growth of a function

Thanks,

LaTeX Code: x^{\\sqrt{x}} is such a function.
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Old Nov28-09, 11:03 PM                  #4
hamster143

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Re: growth of a function

Or LaTeX Code: e^{\\sqrt{x}} , or LaTeX Code: e^{x/\\ln{x}} .
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Old Nov29-09, 09:31 AM                  #5
Jarle

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Re: growth of a function

I'm sure we can find many as you pointed out.
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