       • To: mathgroup at smc.vnet.net
• Subject: [mg55511] Questions about Abs[_]
• From: "Steeve Brechmann \(schumi\)" <steevebrechmann at yahoo.ca>
• Date: Sun, 27 Mar 2005 02:42:44 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

```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-(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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