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MathGroup Archive 2001

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Re: Changing Pure Function in Module

  • To: mathgroup at smc.vnet.net
  • Subject: [mg29842] Re: [mg29822] Changing Pure Function in Module
  • From: Ranko Bojanic <bojanic at math.ohio-state.edu>
  • Date: Fri, 13 Jul 2001 04:19:22 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com


Hi Wilson:
Now that we know exactly what you want, it is easy to write a module for FindD:

FindD[n_]:=Module[{c=1,a},If[IntegerQ[Sqrt[n]],a="n is a perfect square",                           
      While[JacobiSymbol[(-1)^(c+1)(2c+3),n]?-1,c=c+1];
                                a=(-1)^(c+1)(2c+3)];
                            Return[a]]
                            
FindD[1929321]
n is a perfect square

FindD[567134594567891251143216731]
-15

Regards,
Ranko

In Message 42/124 From Flip at safebunch.com Jul 12,01 02:52:35 AM-0400
Wilson wrote:

> Hi All,
> 
> thank you to all who continue to respond to all of my questions ... and there
> are always plenty of them.
> 
> I have the following function embedded in the findD code below.
> 
> a[1] =5;
> 
> a[n_]:= a[n] = (-1)^(n+1) (Abs[a[n-1]]+2)
> 
> In[225]:=
> findD[n_]:=
> Module[{c=0},NestWhile[(c++;(-1)^c(Abs[#]+2))&,5,JacobiSymbol[#,n]!=-1&]]
> 
> I would like to change the pure function to use the following (cleaner) function
> that requires no starting value (and starts for n = 1).
> 
> In[255]:=
> a[n_]:= a[n]= (-1)^(n+1)*(2n + 3)
> 
> Also, it would be important to test n prior to calling findD.  If n is a perfect
> square, findD will "never" converge.  Is there a simple way to test if n is
> square and tell the user ... try again ... n is a perfect square.
> 
> Again thank you for all of the help ... Wilson
> 
> 
> 



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