mahout-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Jake Mannix <>
Subject Re: Taste-GenericItemBasedRecommender
Date Fri, 04 Dec 2009 18:04:06 GMT
On Fri, Dec 4, 2009 at 12:33 AM, Sean Owen <> wrote:

> (Though I'm curious how this works -- looks deceptively easy, this
> outer product approach. Isn't v cross v potentially huge? or likely to
> be sparse enough to not matter)

v cross v is very huge, but very sparse... *but*

  sum_i  (v_i cross v_i)

is indeed going to get pretty dense, so the reducer may totally blow
up if care is not taken - because it's all being done in memory in the
reducer (ie yes, all of A'A lives in memory just before the reducer
completes, in my naive impl).

> I understand the final step in principle, which is to compute (A'A)h.
> But I keep guessing A'A is too big to fit in memory? So I can
> side-load the rows of A'A one at a time and compute it rather
> manually.

How would you do this?  Take the rows of v_i cross v_i and add them
up?  Isn't that another MR job?


  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message