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MathGroup Archive 1992

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Stupid Logs

  • To: mathgroup at yoda.physics.unc.edu (Mathematica User's Group)
  • Subject: Stupid Logs
  • From: Keith Clay <clay at galileo.phys.washington.edu>
  • Date: Thu, 25 Jun 92 15:06:04 MDT

Question: Why is Mathematica's Log function so stupid when there is so much 
	  intelligence in the trig functions?

A few of us have noticed tha Mathematica is at a loss for simplifying even the 
simplest functions involving logarithms.  

Two examples follow.

1) Try asking Mathematica to simplify

	Log[(1+2x+x^2)/(1-x^2) - x/(1-x)] + Log[1-x]

   It will simplify the first Log ARGUMENT to be 1/(1-x), but it doesn't seem
	to know that Log[1/a_]:=-Log[a].
	You can Unprotect Log and tell it this, but why do we have to?

2)  Mathematica is completely at a loss as to how to simplify the following.

> 
>                                                          2
>                       19683 a                      (96 Pi )/l   2
> >         2 l Log[----------------])) / (67108864 E           Pi ) +
>                               2
>                         (48 Pi )/l
>                   1024 E
> 
`	You can probalby simplify it in your head, but unprotecting and redefining
	all of the rules that are needed takes forever.


DOES ANYBODY KNOW A SIMPLE WAY TO DO THIS???

Keith





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