[R] multiplying a matrix by a vector

[Jeff Newmiller]

If you want to get a comparable result, then run the same code. You may not want a comparable result though... your version straightens out the issue Peter was puzzled by. 
-- 
Sent from my phone. Please excuse my brevity.

On November 4, 2016 11:35:02 AM PDT, Berend Hasselman <bhh at xs4all.nl> wrote:
>
>> On 4 Nov 2016, at 19:27, Berend Hasselman <bhh at xs4all.nl> wrote:
>> 
>>> 
>>> On 4 Nov 2016, at 16:41, Jeff Newmiller <jdnewmil at dcn.davis.ca.us>
>wrote:
>>> 
>>> Sara wins on memory use.
>>> 
>>> Rui wins on speed.
>>> 
>>> Bert wins on clarity.
>>> 
>>> library(microbenchmark)
>>> 
>>> N <- 1000
>>> x <- matrix( runif( N*N ), ncol=N )
>>> y <- seq.int( N )
>>> 
>>> microbenchmark( { t( y * t(x) ) }
>>>             , { x %*% diag( y ) }
>>>             , { sweep( x, 2, y, `*` ) }
>>>             )
>>> Unit: milliseconds
>>>                       expr       min        lq    median        uq  
>   max neval
>>>        {     t(y * t(x)) }  6.659562  7.475414  7.871341  8.182623
>47.01105 100
>>>      {     x %*% diag(y) }  9.859292 11.014021 11.281334 11.733825
>48.79463 100
>>> {     sweep(x, 2, y, `*`) } 16.535938 17.682175 18.283572 18.712342
>55.47159 100
>> 
>> 
>> I get different results with R3.2.2 on Mac OS X (using reference
>BLAS).
>> 
>
>Correction: I meant R3.3.2
>
>Berend