Re: Bugs in Abs and Sign !?
- To: mathgroup at smc.vnet.net
- Subject: [mg25676] Re: Bugs in Abs and Sign !?
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Thu, 19 Oct 2000 04:35:09 -0400 (EDT)
- Organization: Universitaet Leipzig
- References: <email@example.com>
- Sender: owner-wri-mathgroup at wolfram.com
Hi, Abs[x^2] is simplifyed first to Abs[x]^2 and *than* your rule Abs[u_]:> fnt[u] is applied. The thame thing happens with Sign[x^2] that is transformed to Sign[x]^2. To prevent this simplifications you need Hold and Hold[Abs[x^2]] /. Abs[u_] :> fnt[u] works as expected. Gruss Jens Jack Goldberg wrote: > > Hi group. > > Try, > > Abs[x^2] /. Abs[u_] -> fnt[u] > > and > > Sign[x^2] /. Sign[u_] -> fnt[u] > > In each case I get fnt[x]^2. Shouldn't I get fnt[x^2]? After all, > g[x^2] /. g[u_] -> fnt[u] returns fnt[x^2] which is what I have been led > to expect from Mathematica. I am using ver 4.01 on a PowerMac. > > These peculiarities are driving me crazy. This is the fourth "bug" I have > found in just 2 weeks. Please tell me I'm wrong. > > Thanks guys. > > Jack