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MathGroup Archive 2005

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Re: Eliminating Annoying Minus Signs

  • To: mathgroup at smc.vnet.net
  • Subject: [mg58768] Re: [mg58756] Eliminating Annoying Minus Signs
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Sun, 17 Jul 2005 13:03:13 -0400 (EDT)
  • Reply-to: hanlonr at cox.net
  • Sender: owner-wri-mathgroup at wolfram.com

test={-((2*x)/(-1+z)),-((2*y)/(-1+z)),-1};

FullSimplify[test,ComplexityFunction:>(Count[{#},_Times[_Negative,__],?]&)]

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

However, this will likely be undone by any subsequent use of simplification 
with the default ComplexityFunction

%//Simplify

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


Bob Hanlon

> 
> From: "David Park" <djmp at earthlink.net>
To: mathgroup at smc.vnet.net
> Date: 2005/07/17 Sun AM 03:04:06 EDT
> Subject: [mg58768] [mg58756] Eliminating Annoying Minus Signs
> 
> 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/ 
> 
> 


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