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Re: imposing parameter assumptions

• To: mathgroup at smc.vnet.net
• Subject: [mg44195] Re: [mg44184] imposing parameter assumptions
• From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
• Date: Sun, 26 Oct 2003 00:41:49 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

On Saturday, October 25, 2003, at 07:26 PM, drr7 wrote:

> Simple question:  How do I impose assumptions on the sign of 
> parameters in
> symbolic equations and then test for the sign of an expression. 
> Example:
> suppose I want to test the sign of f[a]=a^-3 if a<0.  I tried 
> combinations
> of Refine and Positive, but that does not seem to work for me.  What I 
> am
> really trying to do is sign a long expression for a derivative.
> Thanks.
>
>
>
>
Do you mean


Simplify[Sign[a^3-3],a<0]


-1

?

Andrzej Kozlowski
Yokohama, Japan
http://www.mimuw.edu.pl/~akoz/