Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2003
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2003

[Date Index] [Thread Index] [Author Index]

Search the Archive

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

  • To: mathgroup at smc.vnet.net
  • Subject: [mg39327] Re: [mg39303] Simplify[Abs[x],x<0]]
  • From: Tomas Garza <tgarza01 at prodigy.net.mx>
  • Date: Tue, 11 Feb 2003 04:42:34 -0500 (EST)
  • References: <200302100607.BAA23841@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

I do not wish to appear flippant, but if you wish to calculate Abs[x] and
you know that x < 0, then evaluate Abs[-x] with the assumption that x >0:
Abs[x] given that x <0 is equal to Abs[-x] given x > 0.

In[1]:=
Simplify[Abs[-x], x > 0]
Out[1]=
x

Or else, use

In[2]:=
Simplify[ComplexExpand[Abs[x]], x < 0]
Out[47]=
-x

to make sure you are talking of real x (I presume).

Tomas Garza
Mexico City
----- Original Message -----
From: "Uri Zwick" <zwick at cs.tau.ac.il>
To: mathgroup at smc.vnet.net
Subject: [mg39327] [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
>
>
>




  • Prev by Date: RE: Simplify[Abs[x],x<0]]
  • Next by Date: Yet another incorrect integral
  • Previous by thread: Simplify[Abs[x],x<0]]
  • Next by thread: Re: Simplify[Abs[x],x<0]]