Re: Prime[x] crashes kernel for large x

• To: mathgroup at smc.vnet.net
• Subject: [mg7926] Re: [mg7762] Prime[x] crashes kernel for large x
• From: esw at harrier.fen.bris.ac.uk (Eddy)
• Date: Wed, 23 Jul 1997 15:46:06 -0400
• Organization: University of Bristol, England
• Sender: owner-wri-mathgroup at wolfram.com

For Mma 2.0, a calculation may depend on previous calculation.  As you've
already tested, the timing of a calculation after the first one may give
zero time.  It is stated on "Mathematica: A System for Doing Mathematics
with Computer" for version 2.0, and I'm sure it's also stated on the book
for version 3.0.

===
-Eddy

Richard Finley (trfin at fiona.umsmed.edu) wrote:
> I get the same problem with Mma 3.0 (on a Pentium Pro 200 Win95 system) .. I
> have to restart the kernel before proceeding.  One other curiosity, I was
> trying to find out approximately what size number would cause it to crash
> and I noted that 2^26 was OK but 2^27 consistently crashes.  I started
> walking up from 2^26 + 40000000 and found that if I go from that to
> 2^26+50000000 it crashes, but if I perform consecutive trials from 40000000
> in steps of 1000000 I can continue to at least 150000000 (which is greater
> than 2^27) without crashing (that's where I ran out of patience...I don't
> know how far it would have continued.) Why computing Prime[n+k] should
> depend on whether you computed Prime[n] in the previous calculation is
> beyond my understanding of Mma but it is certainly true.  For example, if I
> compute Prime[2^26 + 40000000]//Timing  , it takes 8.47 sec the first time
> you do it, but if you compute it again it gives 0. sec.  It appears it
> "remembers" previous calculations and I presume it somehow uses the results
> in computations of larger primes...so Prime[2^26 + 50000000] crashes only if
> you didn't perform Prime[2^26 + 49000000] etc..first. Do others get the same
> result on other platforms? Any ideas from anyone ? -- Wolfram ?
> RF

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