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MathGroup Archive 2000

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Re: Pattern Matching

  • To: mathgroup at smc.vnet.net
  • Subject: [mg23846] Re: Pattern Matching
  • From: Brian Higgins <bghiggins at ucdavis.edu>
  • Date: Mon, 12 Jun 2000 01:17:36 -0400 (EDT)
  • References: <8hsu3g$dh4@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Johannes, Try the following pattern

x[_]b[_] + __ -> z

It seems to work on the expressions I tried:

g=Sin[x]^2/(b[1]*x[1] + b[2]*x[2] + b[3]*x[3] + b[4]*x[4] +
  b[5]*x[5] + b[6]*x[6])

g/.x[_]b[_] + __ -> z

Sin[x]^2/z

Cheers,

Brian

In article <8hsu3g$dh4 at smc.vnet.net>,
  "Johannes Ludsteck" <ludsteck at zew.de> wrote:
> Dear Group Members,
> I would like to "find" and replace expressions with the simple
> structure x[1] b[1]+x[2] b2]+...+x[n] b[n]
> I tried to use the following replacement rule
> In[27]:= x[1] b[1] + x[2] b[2] /. Plus[Times[x[_], b[_]] ..] -> z
>
> Out[27]= b[1] x[1] + b[2] x[2] + b[3] x[3]
> Which didn't work (Out[27] should be z).
> Why?
> The following FullForm seems to give exactly the structure I used
> in my replacement rule.
>
> In[17]:=
> FullForm[x[1] b[1] + x[2] b[2] + x[3] b[3]]
> Out[17]//FullForm=
> Plus[Times[b[1], x[1]], Times[b[2], x[2]], Times[b[3], x[3]]]
>
> Even if this worked, my pattern wouldn't account for equal
indices,
> i.e. it would match x[1] b[500]+x[12] b[3], even if it shouldn't.
>
> Any suggestions?
> Thanks,
> 	Johannes Ludsteck
>
> Johannes Ludsteck
> Centre for European Economic Research (ZEW)
> Department of Labour Economics,
> Human Resources and Social Policy
> Phone (+49)(0)621/1235-157
> Fax (+49)(0)621/1235-225
>
> P.O.Box 103443
> D-68034 Mannheim
> GERMANY
>
> Email: ludsteck at zew.de
>
>


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