Re: Finding a relative prime (corrected)

*To*: mathgroup at smc.vnet.net*Subject*: [mg19697] Re: [mg19682] Finding a relative prime (corrected)*From*: "Andrzej Kozlowski" <andrzej at tuins.ac.jp>*Date*: Sat, 11 Sep 1999 16:36:04 -0400*Sender*: owner-wri-mathgroup at wolfram.com

Sorry, I answered to quickly and misunderstood your question. Of course you want a number relatively prime to q , not a prime number. So the correct code is: randompick[q_?PrimeQ] := Module[{l}, (l = Select[Range[2, q - 1], GCD[q, #] == 1 &])[[Random[ Integer, {1, Length[l]}]]]] E.g: In[23]:= randompick[Prime[1000]] Out[23]= 552 Actually one can simplify this a bit by using th ebuilt in function EulerPhi, where EulerPhi[n] is the number of positive integers less than n which are relatively prime to n. Then the code becomes: randompick[q_?PrimeQ] := Select[Range[2, q - 1], GCD[q, #] == 1 &][[Random[Integer, {1, EulerPhi[q] - 1}]]] -- Andrzej Kozlowski Toyama International University JAPAN http://sigma.tuins.ac.jp http://eri2.tuins.ac.jp ---------- >From: Timur Tabi <nospam_timur at tabi.org> >To: mathgroup at smc.vnet.net >Subject: [mg19697] [mg19682] Finding a relative prime >Date: Thu, Sep 9, 1999, 3:19 PM > > 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? > > -- > Remove "nospam_" from my email address when replying > Timur "too sexy for my code" Tabi, timur at tabi.org > > > Sent via Deja.com http://www.deja.com/ > Share what you know. Learn what you don't. > >