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RE: Simplify[Abs[x],x<0]]

• To: mathgroup at smc.vnet.net
• Subject: [mg39307] RE: [mg39303] Simplify[Abs[x],x<0]]
• From: "Florian Jaccard" <jaccardf at eicn.ch>
• Date: Tue, 11 Feb 2003 04:40:41 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

Hello !

I don^t know why...
But I also notices that it is better to make your own "abs" :

myAbs[x_]:=Sqrt[x^2]
This one is very good on real numbers !
but if you want to use for example FourierSeries or Laplacetransform, it is
better to use the following :
myAbs[x_]:=UnitStep[x]x-UnitStep[-x]x

Meilleures salutations

Florian Jaccard
professeur de Mathématiques
EICN-HES
7, av. de l'Hôtel-de-Ville
2400 Le Locle
tél. centrale +41 32 930 30 30
tél. direct +41 32 930 35 52
e-mail : jaccardf at eicn.ch


-----Message d'origine-----
De : Uri Zwick [mailto:zwick at cs.tau.ac.il]
Envoyé : lun., 10. février 2003 07:08
À : mathgroup at smc.vnet.net
Objet : [mg39303] Simplify[Abs[x],x<0]]


Hi,

Simplify[ Abs[x] , x>0 ] returns x.
But, Simplify[ Abs[x] , x<0] returns Abs[x], and not -x.

Why is that?

Uri