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MathGroup Archive 2006

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Re: Memory operations

  • To: mathgroup at
  • Subject: [mg64929] Re: Memory operations
  • From: Maxim <m.r at>
  • Date: Wed, 8 Mar 2006 00:59:40 -0500 (EST)
  • References: <dujr2t$8pr$>
  • Sender: owner-wri-mathgroup at

On Tue, 7 Mar 2006 11:33:49 +0000 (UTC), <sir_puding at> wrote:

> Hi.
> Can anyone tell me how to free memory in Mathematica.
> I have some list operations in cycle (really long cycle).
> Smth. like
> -----------------------
> ar={};
> For[i=0,++i<10000000000,
> ar=Append[ar,{bla bla bla}];
> ]
> -----------------------
> How can i free memory allocated for ar  when cycle is completed --- i
> have terrible memory leakage (several megs in minute), cause when I use  
> Clear or Remove ar does
> not point to any address, but the result of previous calculations is
> still in memory. I could not find any operation like free() in C.
> Tnx.

This is due to a strange glitch that appears when For returns the value to  
the top level:

In[1]:= out1 = For[i = 1, i <= 5, i++, 0]

In[2]:= {out1, %}

Out[2]= {Null, Null}

In[3]:= out2 = For[i = 1, i <= 5, i++;, 0]

In[4]:= {out2, %}

Out[4]= {Null, 5}

The result of i++ is stored in DownValues[Out]. So in your case even after  
Clear[ar] the memory taken by the structure is not deallocated because  
there is still a reference to it from DownValues[Out]. Either set  
$HistoryLength = 0 or rewrite your For loop in a different way.

Maxim Rytin
m.r at

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