From: Nameeta Lobo <nlobo_at_bsd.uchicago.edu>

Date: Wed 17 May 2006 - 00:50:51 EST

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Date: Wed 17 May 2006 - 00:50:51 EST

thanks a million for all your extremely prompt responses. This is really appreciated.

Quoting Marc Schwartz <MSchwartz@mn.rr.com>:

> On Tue, 2006-05-16 at 09:45 +0200, Uwe Ligges wrote:

*> > Nameeta Lobo wrote:
**> >
**> > > Hello all
**> > >
**> > > thank you very much for all your suggestions. I actually need binary
**> > > representations. I tried all the methods that Marc,Jim and Charles have
**> > > suggested and they ran fine(thanks a lot). I tried doing it then with 26
**> and 13
**> > > and that's when the computer gave way. I just got a message with all
**> three
**> > > methods that a vector of .....Kb cannot be allocated. guess I will have
**> to
**> > > change the environment to allow for huge vector size allocation. How do I
**> do that?
**> >
**> >
**> > You should have *at least* 512Mb in your machine for the solution given
**> > by Charles C. Berry with the numbers given above, better a machine with
**> 1Gb.
**> >
**> > Uwe Ligges
**>
**> In addition to Uwe's comment, there are some practical issues that will
**> apply here shortly if Nameeta continues to increase the size of the
**> source vector:
**>
**> 1. R has a limitation of 2^32 - 1 elements in a vector. This is the same
**> for both 32 and 64 bit platforms. Thus, if Nameeta is planning to
**> continue to expand the upper limit of the range, you will hit this
**> fairly quickly. You would then need to consider some form of a
**> partitioning approach if you go beyond that limit.
**>
**> 2. The RAM requirements to simply apply Charles' solution will continue
**> to expand as the upper limit increases, so Uwe's figure is but one
**> number that solves the indicated example of 2^26, but will be
**> insufficient beyond that.
**>
**> 3. This still does not address Nameeta's now explicitly stated desire
**> for the binary character representations, which requires additional
**> memory beyond that required for the initial step of identifying the
**> numbers that meet the 'bit requirements' alone.
**>
**> >From my prior post over the weekend, to store the character matrix of
**> binary representations for 2^25 with 9 bits, which contained 2,042,975
**> values, it required approximately 128 Mb for the final paste()'d
**> versions of the numbers.
**>
**> That is AFTER doing the initial conversion using digitsBase(), which
**> required 400 Mb to store the intermediate integer matrix result. One
**> could certainly do that in a partitioned or loop based approach to
**> conserve memory, but it still will hit practical limits in short order.
**>
**> Those figures too will expand dramatically as the upper limit increases.
**>
**> For example, going from 2^24 with 12 bits to 2^26 with 13 bits, results
**> in going from 2,704,156 values in the result to 10,400,600 in the
**> result. That's a 3.8 fold increase in the result vector size. It does
**> not take long to figure out how much memory will be required for these
**> operations as the upper range increases.
**>
**> Depending upon what Nameeta is planning to do with the final resultant
**> character vectors, one could consider a loop based print method/function
**> that takes the values in the initial 'dec.index' vector and simply
**> cat()'s them to some output. However, you would not be able to actually
**> store them as a single matrix given the memory requirements.
**>
**> Perhaps Nameeta can indicate what the primary problem is here, which
**> might in turn allow someone to offer an alternative approach that is
**> more resource sparing.
**>
**> HTH,
**>
**> Marc Schwartz
**>
**>
**>
**>
**>
*

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