Re: Those Pesky Minus Signs
- To: mathgroup at smc.vnet.net
- Subject: [mg43302] Re: [mg43275] Those Pesky Minus Signs
- From: Selwyn Hollis <selwynh at earthlink.net>
- Date: Sun, 24 Aug 2003 04:54:58 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
David,
Here's a rule that may be useful:
pullMinus :=
HoldPattern[(c_.)*Plus[x:Times[_?Negative, _] ..] ] :>
With[{r = Plus @@ {x}[[All,2]]}, HoldForm[-(c*r)]]
-1/2(a + b + c)
1/2(-a - b - c)
% /. pullMinus
-1/2(a + b + c)
-----
Selwyn Hollis
http://www.math.armstrong.edu/faculty/hollis
On Saturday, August 23, 2003, at 08:09 AM, David Park wrote:
> Dear MathGroup,
>
> How would one simplify
>
> (-1/2)(a + b + c)
> 1/2(-a - b - c)
>
> so the minus sign was in front? Why does it get pulled within in the
> first
> place?
>
> David Park
> djmp at earthlink.net
> http://home.earthlink.net/~djmp/
>
>