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MathGroup Archive 2005

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Re: Questions about Abs[_]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55538] Re: [mg55511] Questions about Abs[_]
  • From: yehuda ben-shimol <bsyehuda at gmail.com>
  • Date: Mon, 28 Mar 2005 02:42:15 -0500 (EST)
  • References: <200503270742.CAA06213@smc.vnet.net>
  • Reply-to: yehuda ben-shimol <bsyehuda at gmail.com>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,
The expression you gave in your post is erroneous so I cannot evaluate
what the problem there but for the question for the Abs[] funciton it
is working as expected on my computer (ver. 5.1, Win XP), i.e.
Abs[2a c + 2b d] // Simplify
returns
2 Abs[a c + b d]
and
Abs[(2a c + 2b d)^2] // Simplify
returns
4*Abs[a*c + b*d]^2

yehuda

On Sun, 27 Mar 2005 02:42:44 -0500 (EST), Steeve Brechmann (schumi)
<steevebrechmann at yahoo.ca> wrote:
> 
> Hi,
> 
> I define,
> 
> G0[r_List, r0_List]:=(Exp[I k Norm[r-r0]/(4*Pi*Norm[r-r0]))*((1+(I/(k*Norm[r-r0]))-(1/(k^2*Norm[r-r0]^2)))*IdentityMatrix[3]-(1/Norm[r-r0]^2)*(1+((3*I)/(k*Norm[r-r0]))-(3/(k^2*Norm[r-r0]^2)))*Outer[Times,r-r0,r-r0])
> 
> where
> 
> r = {x,y,z}
> r0={x0,y0,z0}
> ri={x0,y0,-z0}
> rsn=r0+{0,0,2*n*d}
> rim=ri+{0,0,2*m*d}
> 
> When i want to compute
> 
> G0r0rim=G0[r0,rim]
> 
> I find something odd...
> 
> 1) Why Abs[2*z0-2*d*m] doesn't give 2*Abs[z0-m*d] ?
> 
> 2) Why Abs[2*z0-2*d*m] doesn't simplify with (2*z0-2*d*m)^2 ?
> 
> Note : all the variables are positive, i.e. : z0>0, d>0 and -Infinity < m_Integer < Infinity.
> 
> Steeve Brechmann
> Physics Department, Laval University
> steevebrechmann at yahoo.ca
> 
>


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