Comments on: R-Sessions 28: Impressive R Speeds

By: Index of the R-Sessions | Curving Normality

Index of the R-Sessions | Curving Normality — Thu, 24 Mar 2011 09:33:46 +0000

[…] Impressive R Speeds […]

By: Rense Nieuwenhuis

Rense Nieuwenhuis — Mon, 05 Jan 2009 20:19:51 +0000

Hi there, Yason,

Indeed, I’ve been puzzled by this one as well. But, fear not: your computer does not travel back in time

Instead, what is represented here, is that your computer has more than a single core, and that apparently some matrix-calculations are distributed over these multiple cores. Thus, in one second of user time, more than a single second-worth of computing time can take place.

By: Yason

Yason — Mon, 05 Jan 2009 19:25:40 +0000

I don’t quite understand why elapsed time is greater than user+system times in the above examples. In the blog entry you’ve linked in the article, it sound more logical to me: elapsed>user+system. The same is in my experiment (below):

CPU: Intel Core2Duo @ 3.15GHz
L2 Cache: 6Mb
RAM: 4Gb (2x2Gb) @ 800MHz
OS: Windows XP Pro x64
R: 2.8.1 (with Rblas.dll from Athlon64_SSE3)

> system.time(for(i in 1:25) X%*%X)
user system elapsed
6.97 0.13 7.32
> system.time(for(i in 1:25) solve(X))
user system elapsed
6.97 0.17 7.50
> system.time(for(i in 1:10) svd(X))
user system elapsed
34.39 0.41 36.25

By: Jeff

Jeff — Fri, 28 Nov 2008 04:00:03 +0000

> set.seed(123)
> X system.time(for(i in 1:25) X%*%X)
user system elapsed
8.196 0.613 5.256
> system.time(for(i in 1:25) solve(X))
user system elapsed
8.568 1.436 6.856
> system.time(for(i in 1:10) svd(X))
user system elapsed
36.042 4.270 55.122

Hardware Overview:

Model Name: MacBook Pro
Model Identifier: MacBookPro4,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.4 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 3 MB
Memory: 2 GB