Re: How to keep things real?
- To: mathgroup at smc.vnet.net
- Subject: [mg25116] Re: [mg25084] How to keep things real?
- From: Cheng Liu <cliu at lanl.gov>
- Date: Sun, 10 Sep 2000 03:14:38 -0400 (EDT)
- References: <200009080228.WAA01458@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hi, Jos,
Since z appears in the integration limit, the Assumptions in
the Integrate command has no effect on it. You can use the construct
Simplify[expr, assump] in your case:
Simplify[Integrate[x/Sqrt[x^2 + zp^2]^3, {zp, z, Infinity}], x>0&&z>0]
Cheng
>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
--
***********************************************
Cheng Liu
MST-8, MS-G755
Materials Science and Technology Division
Los Alamos National Laboratory
Los Alamos, NM87545
e-mail: cliu at lanl.gov
Phone: (505)665-6892
Fax: (505)667-8021
***********************************************
- References:
- How to keep things real?
- From: Jos Bergervoet <bergervo@iaehv.iae.nl>
- How to keep things real?