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MathGroup Archive 2007

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Re: PowerMod[] - Mathematica 5.0 - problem/error/bug?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg73040] Re: PowerMod[] - Mathematica 5.0 - problem/error/bug?
  • From: dh <dh at metrohm.ch>
  • Date: Tue, 30 Jan 2007 23:32:33 -0500 (EST)
  • References: <epn9t2$chv$1@smc.vnet.net>


Hi Anton,

$Version -> 5.1 for Microsoft Windows (October 25, 2004)

with this version it works just fine.

Daniel



Anton Vrba wrote:

> In Mathematica 5.0 I found on my system the following incorrect result regarding the PowerMod[] function

>    

>   You agree that PowerMod[2,17 p, p]=2^17 for p prime and p>2^17 

>    

>   Mathematica 5.0 calculates PowerMod[2,17 p, p] as 2^2 

>   for p=126322571 through to p=2147483647. (one can change the 2 to any base and the wrong answer base^2 is calculated)

>    

>   below the notebook file converted to text format.

>    

>   Have I a problem in my system? or is this a Mathematica 5.0 bug or possibly a new Pentium bug? 

>    

>   best regards

>   Anton

>    

>   In[60]:=

>   p=Prime[123456780]

>   y=PowerMod[2,17  p,p]

>   FactorInteger[y]

>   "y is the correct result"

>    

>   p=Prime[103456780]

>   y=PowerMod[2,17  p,p]

>   FactorInteger[y]

>   "y should equal 2^17 and not 2^2" 

>    

>   m=5

>   y=PowerMod[2,(2^(32 m)-1)  p,p]

>   FactorInteger[y]

>   m=12

>   y=PowerMod[2,(2^(32 m)-1)  p,p]

>   FactorInteger[y]

>   "y equal 2^(m+1) is a cute result"

>    

>   Out[60]=2543568329

>   Out[61]=131072

>   Out[62]={{2,17}}

>   Out[63]=y is the correct result

>   Out[64]=2112226087

>   Out[65]=4

>   Out[66]={{2,2}}

>   Out[67]=y should equal 2^17 and not 2^2

>   Out[68]=5

>   Out[69]=64

>   Out[70]={{2,6}}

>   Out[71]=12

>   Out[72]=8192

>   Out[73]={{2,13}}

>   Out[74]=y equal 2^(m+1) is a cute result

>    

>   In[75]:=

>   "here is the range of the error"

>   p=Prime[7181138]

>   FactorInteger[PowerMod[2,17  p,p]]

>   p=Prime[7181138+1]

>   FactorInteger[PowerMod[2,17  p,p]]

>   p=Prime[105097565]

>   FactorInteger[PowerMod[2,17  p,p]]

>   p=Prime[105097565+1]

>   FactorInteger[PowerMod[2,17  p,p]]

>   Out[75]=here is the range of the error

>   Out[76]=126322543

>   Out[77]={{2,17}}

>   Out[78]=126322571

>   Out[79]={{2,2}}

>   Out[80]=2147483647

>   Out[81]={{2,2}}

>   Out[82]=2147483659

>   Out[83]={{2,17}}

>    

> 

> 



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