Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2005
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2005

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Eigensystem Eigenvalues fail for 34x34 sparse matric but not for 33x33

  • To: mathgroup at smc.vnet.net
  • Subject: [mg56433] Re: Eigensystem Eigenvalues fail for 34x34 sparse matric but not for 33x33
  • From: Scott Hemphill <hemphill at hemphills.net>
  • Date: Mon, 25 Apr 2005 01:30:48 -0400 (EDT)
  • References: <d4fi04$frb$1@smc.vnet.net>
  • Reply-to: hemphill at alumni.caltech.edu
  • Sender: owner-wri-mathgroup at wolfram.com

barrowes at alum.mit.edu writes:

> After upgrading to 5.1.1, Eigensystem, Eigenvalues, and Eigenvectors
> fail for the following sparse matrix, but only if the square matrix
> size is >= 34x34. It works fine for 33x33. It works fine for all
> attemped sizes on this type of matrix in 5.1.
> 
> Consider the following 34x34 banded matrix:

Are you using a multiprocessor kernel?  Do you have an SMP machine, or
a single processor with HT?

If so, then you may be running into a case where Mathematica decides to
use multiple threads for matrix size >= 34x34.  If you are running too
new a glibc, then you are using an incompatible thread library.  You can
fix this by putting "export LD_ASSUME_KERNEL=2.4.1" in the script which
invokes Mathematica.

If in addition you only have a single processor with hyperthreading, you
may also which to put the line "export OMP_NUM_THREADS=1" in your script.
This will prevent Mathematica from using multiple threads, which in my
testing, actually slows Mathematica down slightly.

Scott
-- 
Scott Hemphill	hemphill at alumni.caltech.edu
"This isn't flying.  This is falling, with style."  -- Buzz Lightyear


  • Prev by Date: Re: Re: A bug in Integrate ?
  • Next by Date: Mathematica 5.0 notebooks icon gone.
  • Previous by thread: Eigensystem Eigenvalues fail for 34x34 sparse matric but not for 33x33
  • Next by thread: Re: Eigensystem Eigenvalues fail for 34x34 sparse matric but not for 33x33