Hi Sunil, You are correct that the naive code will eagerly produce the full matrix UxV, which may be very large :-)
I think your strategy of extracting rows and columns from U and V is the best one. Row and column extraction for dense matrices in vectorz-clj is very efficient since it just uses strided vectors, as is the dot product operation, so you probably won't see much of a performance overhead from doing it this way. I wouldn't worry about the verbosity - obviously you should encapsulate this logic in a function if you are doing it in many places. Top tip: also remember to use (non-zero-indices W) if you want to know which elements of the sparse matrix are non-zero without iterating over every element Mike. On Tuesday, 16 February 2016 23:17:52 UTC+8, Sunil Nandihalli wrote: > > Hi Everybody, > I am newbie to core.matrix .. I have the following expression > > W -> a large spare matrix of size MxN > U -> a dense matrix of size MxK > V -> a dense matrix of size KxN > > and K << (M,N) > (require [clojure.core.matrix :as m]) > > I want to compute (m/mul W (m/* U V)) > > m/mul computes element-wise product > > m/* computes regular matrix multiplication > > I want to know if the above would compute full-matrix UV .. if it does > then I want to know if there is an elegant way to compute the > spare-resultant matrix without blowing up memory in the intermediate stage > > I am currently just extracting the corresponding rows and columns from U > and V for the elements which are non-zero in W .. but that seems > unnecessarily verbose... > > I am using the vectorz implementation of core.matrix > > Thanks in advance. > > Sunil. > -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
