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Cas bugs in the evaluation of the logarithm?

  1. Sep 30, 2009 #1
    hi,

    can you evaluate [tex]ln(f(x))[/tex] in your favorite cas (where x is a zero of f(x) )? what is the result?
     
    Last edited: Sep 30, 2009
  2. jcsd
  3. Sep 30, 2009 #2

    tiny-tim

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    Welcome to PF!

    Hi ilario980! Welcome to PF! :wink:
    If f(x) < 0, then ln(f(x)) isn't defined.

    Other than that, the limit of ln(f(x)) will be -∞. :smile:
     
  4. Sep 30, 2009 #3
    yes, i know; but what seems to me strange is that i tryed in some cas to evaluate that value and the ouput is not -inf and is different depending on the function f(x)

    after this experience i believe that trust cas may be dangerous...

    I.M.
     
  5. Sep 30, 2009 #4

    tiny-tim

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    Hi I.M.! :smile:

    (btw, it's case, not cas :wink:)

    Did you evaluate it using a calculator?

    When you get near 0 or ∞, a calculator can give rounding errors that make a lot of difference!
     
  6. Sep 30, 2009 #5

    chroot

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    He means "computer algebra system," or CAS.

    - Warren
     
  7. Sep 30, 2009 #6

    tiny-tim

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    ah! :redface:

    thanks, Warren! :biggrin:
     
  8. Oct 1, 2009 #7
    hi Tiny-Tim,
    i was not playing with my calculator keys :smile:
    i was interpreting (superficially, i admit) some data and this behavior was leading me to an erroneous conclusion


    Ilario M.
     
  9. Oct 1, 2009 #8

    Borek

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    Another reason to not trust computers too much.
     
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