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MathGroup Archive 2007

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Re: fastest way to add up a billion numbers

  • To: mathgroup at smc.vnet.net
  • Subject: [mg73937] Re: [mg73880] fastest way to add up a billion numbers
  • From: János <janos.lobb at yale.edu>
  • Date: Sat, 3 Mar 2007 01:11:22 -0500 (EST)
  • References: <200703021141.GAA04040@smc.vnet.net>

On Mar 2, 2007, at 6:41 AM, Raj wrote:

> hi!
>
> Could somebody tell me what would be the fastest way to add up a
> billion numbers(from 1 to 10^9 i.e the first billion numbers) in
> Mathematica?
>
> Ofcourse the answer is n(n+1)/2, but is there any other way in
> Mathematica other than the following one:
>
> Total@@Range[10^9]
>
> Thanks,
>
> Raj
>

Here is a newbie reply:

z[n_] = RSolve[{y[1] == 1,
     y[n] == y[n - 1] + n},
    y[n], n]

Timing[z[10^9]]
{0.0001319999999971344*
    Second,
   {{y[1000000000] ->
      500000000500000000}}}

J=E1nos


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