________________________________
From: Zachary Mayer <zach.mayer at gmail.com>
To: Megh Dal <megh700004 at yahoo.com>
Sent: Tuesday, July 19, 2011 12:57 AM
Subject: Re: [R-sig-hpc] Question on foreach package
Make sure you have a parallel backend enabled and properly configured.
Open task manager while you run the computation and see if both cores are being used.
On Mon, Jul 18, 2011 at 3:25 PM, Megh Dal <megh700004 at yahoo.com> wrote:
As per the documentation of foreach package, if I use "%dopar%" then computation happens parallaly and on the contrary for %do%", it happens?sequentially. Here, I tried both "%dopar%" and "%do%" for one of the examples given in the help page of ?foreach:
a <- matrix(1:1600, 40, 40)
b <- t(a)
system.time(foreach(b=iter(b, by='col'), .combine=cbind) %dopar% ? (a %*% b))
? ?user ?system elapsed?
? ?0.04 ? ?0.00 ? ?0.05?
a <- matrix(1:1600, 40, 40)
b <- t(a)
system.time(foreach(b=iter(b, by='col'), .combine=cbind) %do% ? (a %*% b))
? ?user ?system elapsed?
? ?0.05 ? ?0.00 ? ?0.05?
However?surprisingly, I did not see any improvement in the computation time. I am using windows vista with dual core CPU (I think it is dual core as when I open Task manager -> Performance, I see there are 2 windows for CPU Usage History......... I am correct that it is dual core, right?) Therefore as it is dual core, shouldn't the computation time with "%dopar%" will be half of "%do%"?
Am I missing something?
Your help will be highly appreciated.
Thanks
_______________________________________________
R-sig-hpc mailing list
R-sig-hpc at r-project.org
https://stat.ethz.ch/mailman/listinfo/r-sig-hpc