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: <8sjkr7$g3p@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Jack:
Abs[.] and Sign[.] evaluate before the replacement
Abs[x^2]
Abs[x]^2
Sign[x^2]
Sign[x]^2
Prevent this:
Unevaluated[Abs[x^2]] /. Abs[u_] -> fnt[u]
fnt[x^2]
Unevaluated[Sign[x^2]] /. Sign[u_] -> fnt[u]
fnt[x^2]
--
Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565
"Jack Goldberg" <jackgold at umich.edu> wrote in message
news:8sjkr7$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
>
>