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Re: Assuming to be a real number is useless even in simple cases?

• To: mathgroup at smc.vnet.net
• Subject: [mg63958] Re: [mg63945] Assuming to be a real number is useless even in simple cases?
• From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
• Date: Wed, 25 Jan 2006 08:45:43 -0500 (EST)
• References: <200601240630.BAA23642@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

On 24 Jan 2006, at 07:30, Roberto wrote:

> In[1]:=
> Assuming[x\[Element]Reals, Im[x]]
>
> Out[1]=
> Im[x]
>
> Why it's not zero?
>

Because the Evaluator itself make no use at all of $Assumptions. Only  
functions like Refine, Simplify, FullSimplify and a few others make  
use of them. So
you need:

Assuming[x â?? Reals, Refine[Im[x]]]

0

or


Assuming[x â?? Reals, Simplify[Im[x]]]

0

Andrzej Kozlowski

• References:
  • Assuming to be a real number is useless even in simple cases?
    • From: Roberto <roberto@pop.it>