Mathematica 9 is now available
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: [mg58777] Re: Eliminating Annoying Minus Signs
  • From: Peter Pein <petsie at dordos.net>
  • Date: Mon, 18 Jul 2005 03:21:16 -0400 (EDT)
  • References: <dbd12i$2tc$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

David Park schrieb:
> 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/ 
> 
Hi David,

Try setting $Post appropriate:

In[1]:= $Post = InputForm; (* just for copying to email *)

In[2]:= test = {-((2*x)/(-1 + z)), -((2*y)/(-1 + z)), -1}
Out[2]//InputForm= {(-2*x)/(-1 + z), (-2*y)/(-1 + z), -1}

In[3]:= oldPost = If[ValueQ[$Post], $Post, Identity];
  $Post = Simplify[oldPost[#1],
   ComplexityFunction -> (Count[#1, x_ /; x < 0, Infinity] & )] & ;

In[5]:= test
Out[5]//InputForm= {(2*x)/(1 - z), (2*y)/(1 - z), -1}

hope this helps a bit,
Peter


-- 
Peter Pein
Berlin
http://people.freenet.de/Peter_Berlin/


  • Prev by Date: "2p" in BenchmarkReport[] ?
  • Next by Date: Re: Re: Eliminating Annoying Minus Signs
  • Previous by thread: Re: Eliminating Annoying Minus Signs
  • Next by thread: Re: Re: Eliminating Annoying Minus Signs