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MathGroup Archive 2004

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Re: Nullspace

  • To: mathgroup at smc.vnet.net
  • Subject: [mg49624] Re: Nullspace
  • From: Garry Helzer <gah at math.umd.edu>
  • Date: Sun, 25 Jul 2004 02:55:26 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Mac OS 10.3.4, 2.5 GB RAM, Mathematica 5.0.1  No Problem,


On Jul 24, 2004, at 3:47 AM, DrBob wrote:

> I have the same experience here with WinXP, Mathematica 5.0.1, and 2GB 
> of RAM. NullSpace[T, Method -> OneStepRowReduction] evaluated, but 
> then N[Pi, 10^5] crashed the kernel.
>
> But there are always limits, right?
>
> Bobby
>
> On Fri, 23 Jul 2004 06:01:49 -0400 (EDT), Scott Morrison 
> <scott at math.berkeley.edu> wrote:
>
>> Hi again,
>>
>> I'm using $Version == 5.0 for Microsoft Windows (November 18, 2003).
>>
>> For certain (large) matrices m, NullSpace[m,
>> Method->OneStepRowReduction] causes a bad kernel crash (the kernel 
>> dies,
>> and I get a Windows XP dialog about an error having occured, yada 
>> yada)
>>
>> For example (sorry this is so large; it's a real life example...)
>>
>> T = SparseArray[{{217, 7} -> 1, {217, 8} -> q, {310, 10} -> 1, {310, 
>> 11}
>> -> q, {403, 13} -> 1, {403, 14} -> q, {464, 15} -> 1, {464, 17} -> q,
>>   {495, 16} -> 1, {495, 18} -> q, {589, 19} -> 1, {589, 20} -> q, 
>> {682,
>> 22} -> 1, {682, 23} -> q, {775, 25} -> 1, {775, 26} -> q,
>>   {1178, 5} -> 1, {1178, 7} -> q, {1207, 6} -> 1, {1207, 10} -> q,
>> {1300, 9} -> 1, {1300, 13} -> q, {1394, 12} -> 1,
>>   {1394, 15} -> q, {1580, 18} -> 1, {1580, 21} -> q, {1641, 20} -> 1,
>> {1641, 24} -> q, {1734, 23} -> 1, {1734, 27} -> q,
>>   {1829, 26} -> 1, {1829, 28} -> q, {2140, 3} -> 1, {2140, 5} -> q,
>> {2171, 4} -> 1, {2171, 6} -> q, {2449, 13} -> 1,
>>   {2449, 16} -> q, {2479, 14} -> 1, {2479, 18} -> q, {2510, 15} -> 1,
>> {2510, 19} -> q, {2573, 17} -> 1, {2573, 20} -> q,
>>   {2884, 27} -> 1, {2884, 29} -> q, {2915, 28} -> 1, {2915, 30} -> q,
>> {3134, 2} -> 1, {3134, 3} -> q, {3256, 6} -> 1,
>>   {3256, 9} -> q, {3380, 10} -> 1, {3380, 13} -> q, {3411, 11} -> 1,
>> {3411, 14} -> q, {3659, 19} -> 1, {3659, 22} -> q,
>>   {3690, 20} -> 1, {3690, 23} -> q, {3814, 24} -> 1, {3814, 27} -> q,
>> {4002, 30} -> 1, {4002, 31} -> q, {4189, 3} -> 1,
>>   {4189, 4} -> q, {4251, 5} -> 1, {4251, 6} -> q, {4311, 7} -> 1, 
>> {4311,
>> 10} -> q, {4342, 8} -> 1, {4342, 11} -> q,
>>   {4776, 22} -> 1, {4776, 25} -> q, {4807, 23} -> 1, {4807, 26} -> q,
>> {4933, 27} -> 1, {4933, 28} -> q, {4995, 29} -> 1,
>>   {4995, 30} -> q, {5151, 1} -> 1, {5151, 2} -> q, {5397, 9} -> 1,
>> {5397, 12} -> q, {5522, 13} -> 1, {5522, 15} -> q,
>>   {5552, 14} -> 1, {5552, 17} -> q, {5614, 16} -> 1, {5614, 19} -> q,
>> {5677, 18} -> 1, {5677, 20} -> q, {5769, 21} -> 1,
>>   {5769, 24} -> q, {6081, 31} -> 1, {6081, 32} -> q, {_, _} -> 
>> 0},{6144,32}]
>>
>> On my computer at least, NullSpace[T, Method->OneStepRowReduction]
>> returns the correct answer, but then induces a kernel crash. (Often, 
>> but
>> not always, the kernel only crashes on the *next* input, for example
>> N[Pi,10^5]). Just NullSpace[T] returns the correct answer. Running the
>> same code on $Version == "4.2 for Microsoft Windows (June 5, 2002)" I
>> have no problems.
>>
>> For now I'm just using NullSpace[T], but my experience while using 4.2
>> was that OneStepRowReduction worked much faster for the matrices I was
>> dealing with, so hopefully we'll hear about a fix for this! 
>> (Wolfram!?)
>> In the meantime, I'm offering this as (yet another?) bug in v5 which
>> took an inordinate amount of time to track down, and seems worth
>> watching out for.
>>
>> Scott Morrison
>>
>>
>>
>
>
>
> -- 
> DrBob at bigfoot.com
> www.eclecticdreams.net
>
>
Garry Helzer
gah at math.umd.edu


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