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An approximation for exponential.

  1. Oct 10, 2009 #1
    Is there an approximation for exp(-k*L) with L large but finite??
  2. jcsd
  3. Oct 10, 2009 #2


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    Well, what is
    [tex]\lim_{L \to +\infty} e^{-kL}[/tex]​
    ? Doesn't calculus tell you that limit would be a good approximation?

    (P.S. are you making any assumptions about k? )
  4. Oct 10, 2009 #3
    L is large but finite. No assumptions about k but it is positive.
  5. Oct 10, 2009 #4


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    Power series. Use as many terms as you like to improve accuracy.
    I can't seem to do Latex code, but you'll find it here about a screenfull down.

    Oops - no good for negative exponent!
  6. Oct 10, 2009 #5
    The trouble with that is that you can not say that exp(-k*L)=1+-k*L. you need the entire sum.
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