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Re: negative pattern matching anyone?

• To: mathgroup at smc.vnet.net
• Subject: [mg43766] Re: negative pattern matching anyone?
• From: Paolo Bientinesi <pauldj at cs.utexas.edu>
• Date: Fri, 3 Oct 2003 02:28:51 -0400 (EDT)
• Organization: University of Texas at Austin
• References: <blcqqj$p8h$1@smc.vnet.net> <blgio6$fvm$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

> > Then, is there a way to match both -3 and -a with the same pattern?
> 
> Yes -- use Sign:
> 
>    h[x_] := Abs[-x] /; Sign[x] == -1
>    h[x_] := x^2
> 
> Cheers,
> Paul


Thanks for all the answers, but all of them solve the problem
with two different patterns (basically using ||).

About the Sign suggestion, it doesn't seem to work, since 
Sign[-a] yields -Sign[a]:

h[x_ /; Sign[x] == -1]:= Abs[x]
h[x_]:= x^2

h[-3] is 3

but 

h[-a] is a^2
--
Paolo

pauldj at cs.utexas.edu		        paolo.bientinesi at iit.cnr.it