[R-sig-Debian] Accessto OpenBLAS

Scott Raynaud scott.raynaud at yahoo.com
Wed Feb 29 22:42:46 CET 2012

So I was passing this to my IT department but they have now
abandoned me and I'm left to fend for myself.  I guess I have to 
learn how to do everything on my own now.

I looked at the read.me.  It's pretty cryptic.  How does one link
with -lopenblas to a shared library?  At the bash command line?
Somewhere else?  Where?

My machine has 4 Intel® Xeon® Processor X5650 CPUs.  On
Intel's site they say each CPU has 6 cores and 12 threads.  Of 
course I want to take advatage of that horsepower. It looks like 
the environment variables can be setup when I launch R, correct?
The questions is how?  There are three environment variables.  
Which one should I use?  And how do I get R to pick up
those environment variables.  (I'm usinf Rkward as a front end).

There's some ambiguity in the read.me under known issues.  
It says:

The number of CPUs/Cores should less than or equal to 
8*sizeof(unsigned long). On 64 bits, the limit is 64.
I'm not sure what that implies in terms of my machine.
To what values do I set my environment variables?
----- Original Message -----
From: Dirk Eddelbuettel <edd at debian.org>
To: Scott Raynaud <scott.raynaud at yahoo.com>
Cc: "r-sig-debian at r-project.org" <r-sig-debian at r-project.org>
Sent: Thursday, February 23, 2012 11:31 AM
Subject: Re: [R-sig-Debian] Accessto OpenBLAS

On 23 February 2012 at 09:08, Scott Raynaud wrote:
| So my experiments have confirmed that the binary version of
| OpenBLAS uses onlt two cores.  Should the compiled version
| use more?
| I want figure out which package to utilize mulitiple cores in
| a UNIX environment.  Did some research on this a while back 
| but it's a bit fuzzy right now.  My main concern is there's a 
| warning about BLAS and multiple cores in the install docs.
| Will I run into problems?

Did you see the README?  

  Link with libopenblas.a or -lopenblas for shared library.

  4.1 Set the number of threads with environment variables. for example,
  export OMP_NUM_THREADS=4
  If you compile this lib with USE_OPENMP=1, you should only set OMP_NUM_THREADS environment variable.

Some BLAS libraries can respond to environment variables at run-time: MKL,
GotoBlas and hence OpenBlas.  For others such as Atlas this is fixed at
compile time.


"Outside of a dog, a book is a man's best friend. Inside of a dog, it is too
dark to read." -- Groucho Marx

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