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## [Help-gsl] gsl vs ARPACK++

**From**: |
Rafal Topolnicki |

**Subject**: |
[Help-gsl] gsl vs ARPACK++ |

**Date**: |
Tue, 24 Aug 2010 23:08:52 +0200 |

**User-agent**: |
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.7) Gecko/20100720 Lanikai/3.1.1 |

Hi,

`I need to compute 10% of smallest eigenvalues of huge (3432x3432,
``12870x12870, 184756x184756) real symmetric sparse matrix (over 99,8% of
``elements =0).
``At first I tried to do it using GSL and in first case it take ~160s to
``capure all eigenvalues. Because matrix is extremely sparse I thought
``that it will be faster if I use ARPACK++ instead of gsl. I use function
`
ARluSymStdEig<double> dprob(ilosc_wartosci, matrix, "SM");
dprob.ChangeMaxit(10000000000);
dprob.FindEigenvectors();
where ilosc_wartosci is number of eigenvalues I want to compute.

`It works, but I takes ~129s to compute 10% of all eigenvalues. I thought
``I would be much faster.
`My question is, if gsl is so good, ARPACK++ so bad or am I doing sth wrong.

`BTW, ARPACK++ use sparse matrix in CSC format. Is it possible to write
``matrix with columns consisting only zeros using this code?
`
Rafal

**[Help-gsl] gsl vs ARPACK++**,
*Rafal Topolnicki* **<=**