[R] R matrix multiplication slowdown
eaglek2011 at gmail.com
Thu Jan 26 23:21:07 CET 2017
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
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.
(Macbook Pro running 10.11.6, 16Gb, R v 3.3.1)
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