       Re: Who can help me?

• To: mathgroup at smc.vnet.net
• Subject: [mg26799] Re: Who can help me?
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Wed, 24 Jan 2001 04:18:39 -0500 (EST)
• Organization: Universitaet Leipzig
• References: <94gslj\$r0h@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Hi,

you can't check that 3.2 *10^7 comes out because :

Needs["Algebra`Horner`"]

In[]:=Horner[poly, x] /. x -> 2 + 2 Cos[2*Pi/7] // N[#, 32] &

Out[]=0.0010805607234388904362155532364433

In[]:=poly /. x -> 2 + 2 Cos[2*Pi/7] // N[#, 64] &

Out[]=0.001080560723438890436215553236443338243643338039212992606510426812

Regards
Jens

Jacqueline Zizi wrote:
>
> I'm working on this polynomial linked to the truncated icosahedron:
>
>         -17808196677858180 x +
>         138982864440593250 x^2 - 527304830550920588 x^3 +
>         1301702220253454898 x^4 - 2358155595920193382 x^5 +
>         3347791850698681436 x^6 - 3878279506351645237 x^7 +
>         3764566420106299695 x^8 - 3117324712750504866 x^9 +
>         2229873533973727384 x^10 - 1390372935143028255 x^11 +
>         760794705528035032 x^12 - 367240961907017721 x^13 +
>         157018216115380477 x^14 - 59650776196609992 x^15 +
>         20179153653354540 x^16 - 6086251542996201 x^17 +
>         1637007669992780 x^18 - 392300104078670 x^19 +
>         83589038962550 x^20 - 15782712151030 x^21 +
>         2628070696678 x^22 - 383466859804 x^23 + 48618908986 x^24 -
>         5298021900 x^25 + 489095520 x^26 - 37516324 x^27 +
>         2327268 x^28 - 112200 x^29 + 3945 x^30 - 90 x^31 + x^32;
>
> I'm interested at its value for x-> 2 + 2 Cos [2 [Pi] / 7].
> Taking N [] gives  3.2628184 10^7
>
> But if I simplify  first and then take N[] it gives -0.0390625 +
> 0.0195313 [ImaginaryI]
>
> As it is a polynomial with integer coefficients, and 2 + 2 Cos [2 pi /
> 7] is real too, the result should be real.  So I prefer the 1st
> solution,  but for another reason, I'm not so sure of this result.
>
> A Plot between 3 and 3.5, does not help me  neither to check if the
> value 3.2628184  is good and If I do : polynomial /. x -> 3.2628184
> 10^7, it gives 2.7225238332205106`^240
>
> How could I check the result 3.2628184 10^7 ?
>
> Thanks
>
> Jacqueline

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