RE: Pattern Matching

*To*: mathgroup at smc.vnet.net*Subject*: [mg23856] RE: [mg23826] Pattern Matching*From*: "David Park" <djmp at earthlink.net>*Date*: Mon, 12 Jun 2000 01:17:50 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

> -----Original Message----- > From: Johannes Ludsteck [mailto:ludsteck at zew.de] To: mathgroup at smc.vnet.net > 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, Johannes, I hope you get many different answers to this problem. Here is one solution: e1 = Sum[x[i]b[i], {i, 1, 5}] + x[1]b[500] + x[12]b[3]; e1 /. b[n_]x[n_] -> z /. n_Integer z -> z z + b[500] x[1] + b[3] x[12] David Park djmp at earthlink.net http://home.earthlink.net/~djmp/