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 > >

**References**:**Questions about Abs[_]***From:*"Steeve Brechmann \(schumi\)" <steevebrechmann@yahoo.ca>