Re: How does a rule get applied?
- To: mathgroup@smc.vnet.net
- Subject: [mg12449] Re: [mg12417] How does a rule get applied?
- From: Wouter Meeussen <eu000949@pophost.eunet.be>
- Date: Tue, 19 May 1998 13:31:19 -0400
hi, read the chapter in The Book about evaluation order : things like (1+3) get evaluated before the rule applies. You can prevent it by HoldForm: HoldForm[ x^3 + x^(1+3) ] /. x^(n_) + x^(n_+1) ->0 0 wouter. At 11:15 14-05-98 -0400, Yacine Ait-Sahalia wrote: >Hi, > >I'm having trouble understanding how rules are applied after /. Consider >the following example: > x^a + x^(1+a) /. x^(n_) + x^(n_+1) ->0 > x^3 + x^(1+3) /. x^(n_) + x^(n_+1) ->0 > x^3 /. x^(n_) ->0 > >Out[388]= > 0 > >Out[389]= > 3 4 > x + x > >Out[390]= > 0 > > >Could anyone please explain to me why > > x^a + x^(1+a) /. x^(n_) + x^(n_+1) ->0 > >returns 0 (as expected), whereas > > x^3 + x^(1+3) /. x^(n_) + x^(n_+1) ->0 > >returns > > 3 4 > x + x > >instead of 0? > >Thanks for your help. > > Dr. Wouter L. J. MEEUSSEN w.meeussen.vdmcc@vandemoortele.be eu000949@pophost.eunet.be