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MathGroup Archive 2005

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Re: Pattern gremlins.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55119] Re: Pattern gremlins.
  • From: Peter Pein <petsie at arcor.de>
  • Date: Sun, 13 Mar 2005 04:57:38 -0500 (EST)
  • References: <d0u6kr$kl6$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Josef Karthauser wrote:

> I obviously don't understand patterns like I thought that I did.
> 
> Can someone tell me why this matches,
> 
>     In:		a b c d e f g /. d f :> yes
>     Out:	a b c e f g yes
> 
> but this doesn't,
> 
>     In:		a b c d e f g /. x:d f :> yes
>     Out:	a b c d e f g
> 
> ?
> 
> Joe
> --
> Josef Karthauser (joe at tao.org.uk)	       http://www.josef-k.net/
> FreeBSD (cvs meister, admin and hacker)     http://www.uk.FreeBSD.org/
> Physics Particle Theory (student)   http://www.pact.cpes.sussex.ac.uk/
> ================ An eclectic mix of fact and theory. =================
> 
> 
Hi Joe,

1.) I can just guess, what your intention has been..
 I suppose, you wanted to replace each of "d" and "f" in your product "a
b c d e f g". That can be done by

In[1]:= a*b*c*d*e*f*g /. d | f -> yes
Out[1]= a*b*c*e*g*yes^2

The pattern d|f mathes d or f

2.) There's no need to name the pattern in this case. It can be usefull
in many applications. Say - for example - you don't like functions
beginning with S:

In[2]:= Sin[x]+Cos[x]/.f:Sin[t_]->1/f-Cos[t]Cot[t]
Out[2]= Cos[x]-Cos[x] Cot[x]+Csc[x]

replaces Sin[x], using t (matches x)  and f (the name for Sin[t_]) from
the pattern.

You might want to try the following links:
http://library.wolfram.com/infocenter/Articles/1127/
http://library.wolfram.com/infocenter/Articles/1477/
http://library.wolfram.com/infocenter/Articles/3162/

-- 
Peter Pein
Berlin


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