Re: How does a rule get applied?
- To: mathgroup@smc.vnet.net
- Subject: [mg12459] Re: How does a rule get applied?
- From: Paul Abbott <paul@physics.uwa.edu.au>
- Date: Tue, 19 May 1998 13:31:28 -0400
- Organization: University of Western Australia
- References: <6jf2mg$3vl@smc.vnet.net>
Yacine Ait-Sahalia wrote: > 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? Because 1+3 evaluates to 4 _before_ the pattern-matching is attempted. One general workaround is In[1]:= x^3 + x^(1+3) /. x^(n_) + x^(m_) :>0 /; m-n == 1 Out[1]= 0 Cheers, Paul ____________________________________________________________________ Paul Abbott Phone: +61-8-9380-2734 Department of Physics Fax: +61-8-9380-1014 The University of Western Australia Nedlands WA 6907 mailto:paul@physics.uwa.edu.au AUSTRALIA http://www.pd.uwa.edu.au/~paul God IS a weakly left-handed dice player ____________________________________________________________________