Cas bugs in the evaluation of the logarithm?

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    Cas Logarithm
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Discussion Overview

The discussion revolves around the evaluation of the natural logarithm of a function, ln(f(x)), at points where x is a zero of f(x). Participants explore the behavior of computer algebra systems (CAS) in this context, particularly when f(x) approaches zero or negative values.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants note that ln(f(x)) is not defined if f(x) < 0, and that the limit approaches -∞ as f(x) approaches 0.
  • Others express concern that different CAS yield varying results when evaluating ln(f(x)), suggesting that the outputs can be misleading and not always approach -∞.
  • One participant mentions experiencing rounding errors in calculators when evaluating limits near 0 or ∞, which could affect results.
  • There is a clarification regarding the term "CAS," which stands for "computer algebra system," as opposed to a simple calculator.
  • Participants reflect on the reliability of computers in mathematical evaluations, with some cautioning against over-reliance on them.

Areas of Agreement / Disagreement

Participants generally agree that ln(f(x)) is undefined for negative values of f(x) and approaches -∞ as f(x) approaches 0. However, there is disagreement regarding the outputs provided by different CAS, with some participants questioning their reliability.

Contextual Notes

Limitations include potential rounding errors in calculators and the dependence on the specific function f(x) being evaluated, which may lead to different outputs across various CAS.

ilario980
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hi,

can you evaluate ln(f(x)) in your favorite cas (where x is a zero of f(x) )? what is the result?
 
Last edited:
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Welcome to PF!

Hi ilario980! Welcome to PF! :wink:
ilario980 said:
hi,

can you evaluate ln(f(x)) in your favorite cas (where x is a zero of f(x) )? what is the result?

If f(x) < 0, then ln(f(x)) isn't defined.

Other than that, the limit of ln(f(x)) will be -∞. :smile:
 
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.
 
ilario980 said:
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)

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!
 
He means "computer algebra system," or CAS.

- Warren
 
chroot said:
He means "computer algebra system," or CAS.

- Warren

ah! :redface:

thanks, Warren! :biggrin:
 
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.
 
Another reason to not trust computers too much.
 

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