[R] cannot.allocate.memory.again and 32bit<--->64bit

[Pavel Khomski]

hello!
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i use 32bit.Linux(SuSe)Server, so i'm limited with 3.5Gb of memory
i demonstrate, that there is times to times a problem with allocating of 
objects of large size, for example


0.state (no objects yet created)
------------------------------------

 > gc()
                  used (Mb)    gc trigger (Mb)    max used (Mb)
Ncells   162070  4.4          350000  9.4          350000  9.4
Vcells      59921  0.5          786432  6.0          281974  2.2



1.state:  let create now a vector of large size
--------------------------------------------------

 > my.vector<-rnorm(100000*500)
 > object.size(my.vector)/1024^2
[1] 381.4698
 > 100000*500*8/1024^2   #calculate object.size directly
[1] 381.4697
 > gc()
                      used   (Mb)      gc trigger  (Mb)      max used  (Mb)
Ncells       162257     4.4             350000   9.4             
350000   9.4
Vcells   50060239 382.0      50412232 384.7     50060419 382.0



3.state:  well, let create a matrix of the same size from this vector
--------------------------------------------------------------------------

 > my.matrix<-matrix(my.vector,nrow=100000,ncol=500)
 > gc()
                     used      (Mb)       gc trigger    (Mb)     max 
used    (Mb)
Ncells       162264       4.4           350000        9.4          
350000        9.4
Vcells  100060241  763.4    150315042 1146.9   150060261 1144.9
 > object.size(my.matrix)/1024^2    #calculate object.size directly
[1] 381.4698


so, the matrix actually - according to the used.Mb - needs the same Mb 
as the vector.
but, the trigger.Mb - and i still have problems with understanding of 
this - grows ennormously.
and i can sure, i had received the "cannot allocate  the vector of  
xxxKb"-error  last time, trying the same experiment.

if we know, that the matrix (or array generally) is acctually alloccated 
as a vector (with removed dimensions), why do we need so much trigger.Mb 
for it?

is it a problem for R only on a 32bit? what is the difference with 
recpect to trigger.memory  if i use 64bit (i didn't yet)?


thanks for your advice
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