Mathematica 9 is now available
Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2011

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: log expression not simplified

  • To: mathgroup at smc.vnet.net
  • Subject: [mg115837] Re: log expression not simplified
  • From: Praeceptor <gianluca.cruciani at poste.it>
  • Date: Sat, 22 Jan 2011 03:22:24 -0500 (EST)
  • References: <ih3rec$bhe$1@smc.vnet.net>

Thanks to everybody contributing to this thread. In particular to
Andrzej who turned my attention to the use of complexity functions in
mathematica's simplifying tools.

On 18 Gen, 11:53, Andrzej Kozlowski <a... at mimuw.edu.pl> wrote:

> [...]
> However, it is hard to get it to simplify the expression to -1 because th=
e only way to do so seems to involve temporarily increasing the default com=
plexity. Thus, to get it to work we need a craftily designed custom complex=
ity function, like, for example, this one:
>
> f[expr_] := -2 Count[expr, _Log, {0, Infinity}] + LeafCount[expr]
>
> This function "rewards" Simplify for expanding logs and, in this case, th=
e "incentive" works:
>
> Simplify[Log[a/b]/Log[b/a], Assumptions -> {a > 0, b > a},
>  ComplexityFunction -> f]
>
> -1
>
> [...]
>
> Andrzej Kozlowski


  • Prev by Date: Plot works in Mathematca 7 but not in Mathematica 8
  • Next by Date: Re: Mathematica v8: import a space-delimited table of numbers?
  • Previous by thread: Re: log expression not simplified
  • Next by thread: what's wrong?!!