Services & ResourcesWolfram ForumsMathGroup Archive

[Date Index] [Thread Index] [Author Index]

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?

Thanks in advance,
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

• Follow-Ups:
  • Re: How to keep things real?
    • From: Cheng Liu <cliu@lanl.gov>