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Re: Reducing memory footprint in use of FullSimplify ?
*To*: mathgroup at smc.vnet.net
*Subject*: [mg56182] Re: Reducing memory footprint in use of FullSimplify ?
*From*: Madhusudan Singh <spammers-go-here at spam.invalid>
*Date*: Mon, 18 Apr 2005 03:08:41 -0400 (EDT)
*References*: <4261f768$0$79461$14726298@news.sunsite.dk> <1Dv8e.2568$J12.1938@newssvr14.news.prodigy.com>
*Sender*: owner-wri-mathgroup at wolfram.com
Richard Fateman wrote:
> You may have found a bug in Mathematica where it
> is not reclaiming memory. Perhaps you can write your
> intermediate expressions to files before the system
> crashes, and then re-load only the parts you need.
>
Ok. Somehow I am not surprised. I moved from Mathematica 4.1 to 5.1 a few
days ago. And the frontend has been a little flaky, crashing every now and
then. Which has forced me to use the kernel alone (without the X frontend).
Is there a command that can make Mathematica flush memory that is lost
otherwise ?
>
> It is probably a mistake to use FullSimplify for a lot
> of expressions, since that program can be very costly, and
> it is possible that it is, all by itself, on the last command,
> using too much memory.
No. I am using MemoryInUse[] to monitor the usage of memory after every
FullSimplify operation is over. This increases almost monotonically even
though the variable that it operates on is explicitly set to zero
(replacing a very long expression - something that should free up large
amounts of memory).
Let us say I have
a=FullSimplify[b]
where b is a very long complicated expression and a is a less complicated
expression. Then the following operation :
b=0;
Print[MemoryInUse[]];
after the FullSimplify above, should free up memory(b)-memory(a)+1 (assuming
storing a zero takes one unit of memory) units of memory. However, I find
that the above number is negative (if MemoryInUse[] is to be believed) even
though it is pretty obvious that memory(b) > memory(a).
As you say, that memory should be freed up as soon as it is done. One more
wierd symptom I have noticed with version 5.1 is that if I interrupt a
running Mathematica kernel (quit kernel), an orphaned process named
aaa****** keeps running until I kill that separately using its PID.
I wonder what people at Wolfram have been upto.
>> Is there some way I can force Mathematica to free up memory on the data
>> stack (I am currently setting the unsimplified expression to zero as soon
>> as it is simplified and assigned to another variable) when it is done
>> with an element ?
>
> What do you mean by data stack?
>
Well, I was referring to the size of data in KB that I am allowed (ulimit).
> I assume you are setting expressions assigned to
> Out[] to zero, or clearing them.
I am using $HistoryLength=0. Would that be equivalent ?
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