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[1] = {0, 0, 0, 2, -1}.l; Gap[2] = {0, 0, 1, -2, 1}.l; Gap[3] = {0, 1, -3, 6, -4}.l; Gap[4] = {1, -4, 6, 4, 1}.l; l = RotateRight[l, 1]; l[[5]] = 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[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]] > > > ]

**References**:**Mathematica slows down***From:*George Szpiro <george@netvision.net.il>