How to keep things real?

• To: mathgroup at smc.vnet.net
• Subject: [mg25084] How to keep things real?
• From: Jos Bergervoet <bergervo at iaehv.iae.nl>
• Date: Thu, 7 Sep 2000 22:28:37 -0400 (EDT)
• Organization: Internet Access Eindhoven, the Netherlands
• Sender: owner-wri-mathgroup at wolfram.com

```With the following input:

Integrate[ x/Sqrt[x^2+zp^2]^3, {zp,z,Infinity},
Assumptions -> {x>0, z>0} ]

I get:

2    2             2
Out[1]= x If[x  + z  >= 0 || Im[x ] != 0,   ...., .... ]

Why does this if-statement appear in the output? Why is Mathematica
apparently ignoring my directive that x and z are positive?

The same happens with Assumptions -> {x \[Element] Reals,
z \[Element] Reals}  and with combinations of these two versions.

I would like to have the answer without "if", to use it in
subsequent computations. Is there a way to do this?

Jos

--
Dr. Jozef R. Bergervoet                      Electromagnetism and EMC
Philips Research Laboratories,             Eindhoven, The Netherlands
Building WS01                                     FAX: +31-40-2742224
E-mail: bergervo at natlab.research.philips.com    Phone: +31-40-2742403

```

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