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Assumptions ignored?

  • To: mathgroup at
  • Subject: [mg25061] Assumptions ignored?
  • From: Jos R Bergervoet <Jos.Bergervoet at>
  • Date: Thu, 7 Sep 2000 22:28:03 -0400 (EDT)
  • Organization: Philips Research Laboratories
  • Sender: owner-wri-mathgroup at

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 plain answer (without ifs and whens) to
use it in further computations. How can it be obtained? (If
possible, do not give answers about menus and mouseclicks, but
just the lines of input to be typed. I'm not very fond of GUI's ;-)

Thanks in advance,

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

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