       Re: For loop problem in mathematica

• To: mathgroup at smc.vnet.net
• Subject: [mg90258] Re: For loop problem in mathematica
• From: "Dana DeLouis" <dana.del at gmail.com>
• Date: Thu, 3 Jul 2008 06:14:17 -0400 (EDT)

```>  For[i = 1, i < 10,000,000, i++, x = x + 1/(i^2)];

Just to add.  The "HarmonicNumber" of 10,000,000 is very large to be done
quickly.
If you wish Machine Precision, perhaps another idea:

Timing[Sqrt[6*HarmonicNumber[10000000., 2]]]

{0.`, 3.1415925580968302`}

Just a note:
The Numerator of just 100,000 has about 87,000 digits in it.

HarmonicNumber[100000, 2] // Numerator // IntegerLength

86904

--
HTH :>)
Dana DeLouis
Mathematica 6.01 (Windows Vista)
Having to Read 5.0 Help Files

"PhysNova" <skhoshbinfar at gmail.com> wrote in message
news:g4d2qf\$emo\$1 at smc.vnet.net...
> Hi,
> i wrote a simple program of evaluating Pi number in M6 to test cpu
> computation timing, to do this a simple for loop
>
> was used:
>
> x=0;For[i = 1, i < 10,000,000, i++, x = x + 1/(i^2)];N[Sqrt(6*x),25]//
> Timing
>
> the result was catastrophe! it take few minuates. but i first expect
> to do this very simple job in few
>
> seconds.computation time is just satisfactory up to 100000 cycle.
>
> could anyone interperet this falut?
> our get an idea to improve the result?
>
> Tanks
>

```

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