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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!



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