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From Fernando Fernández <fernando.fernandez.gonza...@gmail.com>
Subject Re: Lanczos Algorithm
Date Tue, 23 Nov 2010 16:32:09 GMT
```Hi Jake,

You say that LanczosSolver leaves the eigenvalues in the reverse order that
I expect, but, at least the eigenvectors are given in the same order, aren't
they? I mean, If I want the top N eigenvalues and eigenvectors, and i ask
for 4N, I should take the last N eigenvalues and the N eigenvectors, right?
I read also that there is an issue regarding the number of eigenvalues and
eigenvectors that are returned when you ask LanczosSolver for N of them, and
I have checked that if I ask for 40, for example, I get only 39. Will this
leave out the biggest eigenvector and eigenvalue or the smallest one, or
none of these? I spent the last weeks reading abouth this in the discussions
but it's not very clear for me yet.

Could you give us some help?

By the way, I'm interested in having Uk  and also V*S(-1) so i'm able to
project new rows into the U space...

2010/11/22 Ted Dunning <ted.dunning@gmail.com>

> That seems like a lot.  That would mean that have 10^14 = 100 trillion
> nonzero elements which would take 10PB to store with one bit per non-zero
> element.
>
> Are there many totally zero rows?
>
> Can you estimate how many non-zero elements you have in all?
>
> On Mon, Nov 22, 2010 at 1:07 PM, PEDRO MANUEL JIMENEZ RODRIGUEZ <
> pmjimenez1983@hotmail.com> wrote:
>
> >
> > Hi Ted,
> >
> > I can't give you an exact amount but more or less it could be around 10^5
> > non-zero elements per row.
> >
> > Could you please let me know, why the lanzcos algorithm is not always
> > returning the values in a decreasing order?
> >
> > Thanks.
> >
> > Pedro.
> >
> > ----------------------------------------
> > > From: ted.dunning@gmail.com
> > > Date: Fri, 19 Nov 2010 13:34:19 -0800
> > > Subject: Re: Lanczos Algorithm
> > > To: user@mahout.apache.org
> > >
> > > How many non-zero elements?
> > >
> > > On Fri, Nov 19, 2010 at 12:34 PM, PEDRO MANUEL JIMENEZ RODRIGUEZ <
> > > pmjimenez1983@hotmail.com> wrote:
> > >
> > > >
> > > >
> > > > I was talking about 10^9 rows and 10^9 columns
> > > >
> > > > ----------------------------------------
> > > > > From: ted.dunning@gmail.com
> > > > > Date: Fri, 19 Nov 2010 12:07:16 -0800
> > > > > Subject: Re: Lanczos Algorithm
> > > > > To: user@mahout.apache.org
> > > > >
> > > > > On Fri, Nov 19, 2010 at 11:17 AM, PEDRO MANUEL JIMENEZ RODRIGUEZ
<
> > > > > pmjimenez1983@hotmail.com> wrote:
> > > > >
> > > > > > In this project I would have to work with matrix of 10^9, which
> > have a
> > > > very
> > > > > > sparse data.
> > > > >
> > > > >
> > > > > I think you mean 10^9 rows and 10^9 columns with much fewer 10^18
> > > > non-zero
> > > > > elements.
> > > > >
> > > > > Is that correct?
> > > > >
> > > > > Can you say how many non-zero elements?
> > > >
> > > >
> >
> >
>

```
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