Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
1999
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 1999

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Re: Finding a relative prime

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19757] Re: [mg19704] Re: Finding a relative prime
  • From: "Frans Martens" <fransm at win.tue.nl>
  • Date: Wed, 15 Sep 1999 03:53:06 -0400
  • Reply-to: fransm at win.tue.nl
  • Sender: owner-wri-mathgroup at wolfram.com

Hello,

Timur Tabi wrote

I'm using Mathematica 3.0 for the Mac, and I'm trying to figure out how
to get it to pick a random number that is relatively prime to another
number, p-1, where p is prime.  In other words, pick a random number k
such that 1) k is between 2 and p-1, and 2) k is relatively prime to p-1.
How can I do that in Mathematica 3.0?


Ken Levasseur used in his solution FixedPoint.

relprime[p_] := 
  FixedPoint[Random[Integer, {2, p - 2}] &, p - 1, 
    SameTest -> ((GCD[p - 1, #2] == 1) &)]

You can also use a recursive function:

Clear[f];
f[p_] /; PrimeQ[p] && p > 3 := 
   (If[GCD[#1, p - 1] === 1, #1, f[p]] & )[Random[Integer, {2, p - 2}]]




Frans Martens
Eindhoven University of Technology
Faculty of Mathematics and Computer Science
P.O.Box 513
5600 MB Eindhoven The Netherlands
Telephone -31402474280 
Telefax -31402436685
E-mail fransm at win.tue.nl


  • Prev by Date: RE: 3DPlots... Also, generalizations to nDPlots, n>3
  • Next by Date: Special 3D Plots
  • Previous by thread: Re: RE: Finding a relative prime
  • Next by thread: contourplots