Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2005
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2005

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

Search the Archive

Re: Eliminating Annoying Minus Signs

  • To: mathgroup at smc.vnet.net
  • Subject: [mg58790] Re: Eliminating Annoying Minus Signs
  • From: Andrzej Kozlowski <akozlowski at gmail.com>
  • Date: Tue, 19 Jul 2005 04:10:01 -0400 (EDT)
  • References: <200507170704.DAA02676@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On 17 Jul 2005, at 08:04, David Park wrote:

> Here is an expression that has annoying minus signs in it.
>
> test = {-((2*x)/(-1 + z)), -((2*y)/(-1 + z)), -1};
>
> We can get rid of them with the following operation.
>
> MapAt[Minus, test, {{1, 1}, {1, 3, 1}, {2, 1}, {2, 3, 1}}]
> {(2*x)/(1 - z), (2*y)/(1 - z), -1}
>
> But it involves ferreting out the two positions at which we want to  
> change signs and so is a little tedious and error prone.
>
> Does someone have a simpler method for simplifying such  
> expressions, which occur quite often with Mathematica?
>
> David Park
> djmp at earthlink.net
> http://home.earthlink.net/~djmp/
>
>


One possible way that will work not only in this case but in other  
cases when what seems to be the "simplest" expression is not chosen  
by Mathematica is to use

VisibleSimplify[expr_, opts___] := Simplify[
     expr, opts, ComplexityFunction ->
(StringLength[ToString[TraditionalForm[#]]] &)]

or

VisibleFullSimplify[expr_, opts___] := FullSimplify[
     expr, opts, ComplexityFunction ->
(StringLength[ToString[TraditionalForm[#]]] &)]


In this case:


VisibleSimplify[test]


{(2*x)/(1 - z), 2/(1 - z), -1}

VisibleSimplify should return the form of an expression that seems  
"simplest" to "the human eye" among all those found by applying the  
default (or user defined) transformation functions.

Andrzej Kozlowski

Wolfson College,
Univ. of Oxford,
UK.



  • Prev by Date: Re: "2p" in BenchmarkReport[] ?
  • Next by Date: What we get from (0.0*x), (0.0^x) and similar stuff
  • Previous by thread: Re: Eliminating Annoying Minus Signs
  • Next by thread: Re: Eliminating Annoying Minus Signs