       Re: Mathematica slows down

• To: mathgroup at smc.vnet.net
• Subject: [mg52966] Re: [mg52956] Mathematica slows down
• From: yehuda ben-shimol <benshimo at bgu.ac.il>
• Date: Sat, 18 Dec 2004 03:59:39 -0500 (EST)
• References: <200412171020.FAA16192@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Hi George,
I couldn't notice any speedup for k>10000 but your program is inefficient
since you are computing the same primes too many times. A faster idea is to
store them
Timing of your program for k=10000 is
44.4062 Seconds
and with the following program the timing is
1.3258 Seconds

l = Table[Prime[i], {i, 5}];
For[k = 1, k < 20001, k++,
Gap = {0, 0, 0, 2, -1}.l;
Gap = {0, 0, 1, -2, 1}.l;
Gap = {0, 1, -3, 6, -4}.l;
Gap = {1, -4, 6, 4, 1}.l;
l = RotateRight[l, 1];
l[] = Prime[k + 5];
];
I can make it more efficient but this will be minor change.
good luck
yehuda

On Friday 17 December 2004 12:20, George Szpiro wrote:
> 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=Prime[k+1]-Prime[k];
>   Gap=Prime[k+2]-2Prime[k+1]+Prime[k];
>   Gap=Prime[k+3]-3Prime[k+2]+3Prime[k+1]-Prime[k];
>   Gap=Prime[k+4]-4Prime[k+3]+6Prime[k+2]-4Prime[k+1]+Prime[k];
>
>   If[Mod[k,1000]==0, Print[ k]]
>
>
>   ]

```

• Prev by Date: An argument pattern problem: ranges and lists
• Next by Date: Re: NIntegrate a list
• Previous by thread: Mathematica slows down
• Next by thread: Re: Mathematica slows down