[R] R matrix multiplication slowdown
Jeff Newmiller
jdnewmil at dcn.davis.ca.us
Fri Jan 27 15:29:54 CET 2017
You are asked by the Posting Guide to provide a reproducible example and to post in plain text (because HTML gets mangled). I would guess your problem has nothing to do with multiplication, but without the code there is no way to say for sure.
--
Sent from my phone. Please excuse my brevity.
On January 26, 2017 2:21:07 PM PST, ken eagle <eaglek2011 at gmail.com> wrote:
>Hi all. A question about performance of matrix multiplication.
>
>
>
>I have two relatively large matrices:
>
>
>
>A is 100x3072, all integers 0-255, not sparse
>
>B is 1016x3072, all integers 0-255, not sparse
>
>
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>The command z<-B %*% t(A) works fine and takes roughly 0.2 seconds .
>If I
>add one row to B, the same command takes 2.4 seconds; at 1050 rows in
>B,
>the command is up to almost 4 seconds. Just trying to understand why
>the
>big slowdown is occurring, especially since the matrices I actually
>want to
>multiply have 1000 and 5000 rows, not 100 and 1017.
>
>
>
>Thanks,
>
>Ken
>
>
>
>(Macbook Pro running 10.11.6, 16Gb, R v 3.3.1)
>
> [[alternative HTML version deleted]]
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