Re: Bugs in Abs and Sign !?
- To: mathgroup at smc.vnet.net
- Subject: [mg25686] Re: Bugs in Abs and Sign !?
- From: "Allan Hayes" <hay at haystack.demon.co.uk>
- Date: Thu, 19 Oct 2000 04:35:15 -0400 (EDT)
- References: <firstname.lastname@example.org>
- Sender: owner-wri-mathgroup at wolfram.com
Jack: Abs[.] and Sign[.] evaluate before the replacement Abs[x^2] Abs[x]^2 Sign[x^2] Sign[x]^2 Prevent this: Unevaluated[Abs[x^2]] /. Abs[u_] -> fnt[u] fnt[x^2] Unevaluated[Sign[x^2]] /. Sign[u_] -> fnt[u] fnt[x^2] -- Allan --------------------- Allan Hayes Mathematica Training and Consulting Leicester UK www.haystack.demon.co.uk hay at haystack.demon.co.uk Voice: +44 (0)116 271 4198 Fax: +44 (0)870 164 0565 "Jack Goldberg" <jackgold at umich.edu> wrote in message news:8sjkr7$g3p at smc.vnet.net... > 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 > >