Re: Pattern Matching

*To*: mathgroup at smc.vnet.net*Subject*: [mg23847] Re: [mg23826] Pattern Matching*From*: Andrzej Kozlowski <andrzej at tuins.ac.jp>*Date*: Mon, 12 Jun 2000 01:17:37 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

The problem is that Plus[Times[x[_], b[_]] ..] evaluates before the pattern matching is performed and Plus disappears from the Pattern (Plus[a] gives a): In[6]:= Plus[Times[x[_], b[_]] ..] Out[6]= b[_] x[_] .. You have to prevent this from happening with HoldPattern: In[7]:= Plus[x[1] b[1] , x[2] b[2] ] /. HoldPattern[Plus[Times[x[_], b[_]] ..] ] -> z Out[7]= z Andrzej -- Andrzej Kozlowski Toyama International University, JAPAN For Mathematica related links and resources try: <http://www.sstreams.com/Mathematica/> on 6/10/00 4:00 PM, Johannes Ludsteck at 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 >