Re: Pattern matching

*To*: mathgroup at smc.vnet.net*Subject*: [mg116220] Re: Pattern matching*From*: "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>*Date*: Mon, 7 Feb 2011 06:05:30 -0500 (EST)*References*: <iilth1$2mk$1@smc.vnet.net>

I guess that when n reaches 0 Mathematica is smart enough to understand that 0*fact[-1] == 0 independent of the value of fact[-1]... Cheers -- Sjoerd On Feb 6, 11:35 am, StatsMath <stats.ma... at gmail.com> wrote: > Have a question regarding the applicaiton of pattern rules: > > fact[4] //. {fact[n_] :> n fact[n-1], fact[0] -> 1} > > This is a bug since fact[0] needs to be defined 1st, but I expected > the above to grind away idefnitely but it returned a a value 0, > instead of an infininte computation. > > Can you help me understand why the above returns 0? > > Thanks!