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Topic: Pattern matching
Replies: 5   Last Post: Feb 21, 2011 4:20 AM

 Messages: [ Previous | Next ]
 Charles Gillingham Posts: 14 Registered: 10/30/10
Re: Pattern matching
Posted: Feb 19, 2011 5:13 AM

There is no way to modify the rule and get the result you expect. f[u+0] becomes f[u] before the rule is even applied. You can modify the way you apply the rule, like so:

rule = f[u + x_ ] :> x

ReleaseHold[ Hold[ f[u+0] ] /. rule ]

Begin forwarded message:

From: "Andr=E9 M. Grabinski"@smc.vnet.net
Date: February 18, 2011 1:33:47 AM
Subject: Pattern matching

Hi everyone,

hopefully someone of you could answer me a simple question concerning
patterns in Mathematica 8. Consider the following minimal example,

In[1]:= rule = f[u + x_] -> x;
f[u + 5] /. rule
f[u + 0] /. rule
f[u] /. rule

Out[1]= 5

Out[2]= f[u]

Out[3]= f[u]

Now the question: in which way do I need to modify "rule" in order to
get "0" as result for "Out[3]"? Of course I could add a second rule,
i.e. "rule = {f[u + x_] -> x,f[u] -> 0}", but I feel like there should
be a more elegant way than to take care of each and every exception
(okay, in this minimal example this wouldn't matter but I'm just
interested in the general way of setting up patterns).

Thank you very much in advance,

A.G.

Date Subject Author
2/18/11 "André M. Grabinski"
2/19/11 lshifr@gmail.com
2/20/11 Alexey
2/21/11 lshifr@gmail.com
2/19/11 Charles Gillingham
2/19/11 Bob Hanlon