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