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MathGroup Archive 2006

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RE: memory issues

  • To: mathgroup at smc.vnet.net
  • Subject: [mg68807] RE: [mg68751] memory issues
  • From: "Virgilio, Vincent - SSD" <Vincent.Virgilio at itt.com>
  • Date: Sat, 19 Aug 2006 00:41:12 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Perhaps this will help answer your last question:

In[1]:=

m=Table[ByteCount[Range[i]],{i,10}]
Rest[m]-Most[m]

Out[1]=

{60,64,68,72,76,80,84,88,92,96}

Out[2]=

{4,4,4,4,4,4,4,4,4}


Each exact integer added to the list (from Range) uses an additional 4
bytes.  Then, 4 * 125*^6 = 500*^6, which is about the memory footprint
you note for DAT below.

Vince Virgilio

(However, I notice ByteCount[{1}] != ByteCount[Range[1], i.e. 40 != 60.
ByteCount does not have Hold attributes, so it shouldn't see
Range[1]---does it somehow?)

-----Original Message-----
From: Christoph Lhotka [mailto:lhotka at astro.univie.ac.at] 
To: mathgroup at smc.vnet.net
Subject: [mg68807] [mg68751] memory issues

Hi!

Running Mathematica 5.2 on 64Bit (AMD) with 2GB of RAM Memory OS:
WindowsXP 64 Pro. I get the message: No more memory available.
Mathematica Kernel has shut down...

How do I find out:

1) How much memory can Mathematica store in the RAM?
2) How much memory can Mathematica store on the Hard disk (swap file)?
3) At which memory limit does Mathematica begin writting to the had
disk?
3) Can I influence these limit 3) using the OS or in Mathematica?
4) How do I find out at which point in the calculation the kernel stops?
5) Why does my dual core processor does not work higher than with 50%

Doing some tests on my own I got the following riddle:

In[]:=ByteCount[1]
Out[]:=16

In[]:=2000000000/16
Out[]:=125000000

In[]:=DAT=Table[i,{i,1,125000000}];

In[]:=ByteCount[DAT]
Out[]:=500000056

In[]:=MaxMemoryUsed[]
Out[]:= 502133312

Why is a list of 125 000 000 different integers (a 16 Byte) only 500 000
000 Bytes long? How should I estimate the memory limits in my
algorithms, when designing them on this basis?

Thank you in advance

Christoph

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