R help - Jan 2006 - efficiency with "%*%"

Hi,

x and y are (numeric) vectors. I wonder if one of the following is more
efficient than the other:

x%*%y

or

sum(x*y)
?

Thanks,
Dimitri Szerman

dimitrijoe at ipea.gov.br wrote:
> Hi,
> 
> x and y are (numeric) vectors. I wonder if one of the following is more
> efficient than the other:
> 
> x%*%y
> 
> or
> 
> sum(x*y)
> ?
I'd try

   x <- rnorm(1000000)
   y <- rnorm(1000000)
   system.time(x%*%y)
   system.time(sum(x*y))

and finally (hint, hint!):

   system.time(crossprod(x, y))

Uwe Ligges

> Thanks,
> Dimitri Szerman
> 
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