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MathGroup Archive 2004

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Re: Mathematica slows down

  • To: mathgroup at smc.vnet.net
  • Subject: [mg52964] Re: [mg52956] Mathematica slows down
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Sat, 18 Dec 2004 03:59:37 -0500 (EST)
  • Reply-to: hanlonr at cox.net
  • Sender: owner-wri-mathgroup at wolfram.com

I don't know what changes; however, you can speed it up by avoiding 
repeated calls of Prime for the same values

NumP=15000;

Table[pk[n]=Prime[n],{n,NumP}];

For[k=1,k<NumP,k++,
  Gap[1]=pk[k+1]-pk[k];
  Gap[2]=pk[k+2]-2pk[k+1]+pk[k];
  Gap[3]=pk[k+3]-3pk[k+2]+3pk[k+1]-pk[k];
  Gap[4]=pk[k+4]-4pk[k+3]+6pk[k+2]-4pk[k+1]+pk[k];
  If[Mod[k,1000]==0,Print[k]]]


Bob Hanlon

> 
> From: George Szpiro <george at netvision.net.il>
To: mathgroup at smc.vnet.net
> Date: 2004/12/17 Fri AM 05:20:43 EST
> To: mathgroup at smc.vnet.net
> Subject: [mg52964] [mg52956] Mathematica slows down
> 
> Hello,
> 
> the following program runs ok for the first 6,000 iterations, then slows 
> down considerably, and then seems to speed up again after 10,000. Does 
> anyone know what is going on?
> 
> Thanks,
> George
> 
> 
> NumP=15000;
> 
> For[k=1,k<NumP,k++,
> 
>   Gap[1]=Prime[k+1]-Prime[k];
>   Gap[2]=Prime[k+2]-2Prime[k+1]+Prime[k];
>   Gap[3]=Prime[k+3]-3Prime[k+2]+3Prime[k+1]-Prime[k];
>   Gap[4]=Prime[k+4]-4Prime[k+3]+6Prime[k+2]-4Prime[k+1]+Prime[k];
> 
>   If[Mod[k,1000]==0, Print[ k]]
> 
> 
>   ]
> 
> 
> 


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