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Re: memory


From: Martin Helm
Subject: Re: memory
Date: Tue, 5 Apr 2011 14:03:45 +0200
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Am Dienstag, 5. April 2011, 13:13:21 schrieb nuncio m:
> Hi martin,
>   Here is the code snippet
>         R=f' * f ---------------------------------(1)
>         [C,L]=eigs(R);-----------------------(2)
>     [C1,Lambda,CC]=svd(f);-------------(3)
> 
> memory error is shown at 1
> thanks
> nuncio
> 
> On Tue, Apr 5, 2011 at 4:26 PM, Martin Helm <address@hidden> wrote:
> > Am Dienstag, 5. April 2011, 11:06:09 schrieb nuncio m:
> > > Hi list,
> > > 
> > >     What is the maximum size of a matrix that octave can hold. Why I am
> > > 
> > > asking this is, I am getting a memory when I try to find the eigen
> > > values of a matrix of 348 rows and 29898 columns.   I am using a 32
> > > bit open
> > 
> > suse
> > 
> > > on pentium 4 processor having 2 GB of RAM and a swap of 4.6 GB. Any
> > > help would be greatly appreciated.
> > > 
> > > nuncio
> > 
> > Your matrix is fairly small around 80 MB memory consumption, so no
> > problem in
> > itself at all. The amount of memory you can use depends on your system
> > architecture. With 32 bit you can use up to 2GB for a matrix, with a 64
> > bit (linux) system you can have a matrix up to 16 GB, this limit does
> > not exist if
> > octave is built with 64 bit indexing enabled (but this is still
> > experimental I
> > think).
> > 
> > You say you run out of memory calculating the eigen values of a nonsquare
> > matrix (?). can you show us a short code snippet how you do that? I am
> > not sure if I really understand.
> > Do you calculate something like eig(a'*a) or eig(a*a')? If yes you are
> > better
> > served with looking at the svd command instead of calculating a matrix
> > product.

R is a matrix with 29898^2 entries which is about 7 GB of memory!
What's wrong with simply using svd(f), you just need to square the singular 
values.


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