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## In which functions is used the lapack DGELSY subroutine?

**From**: |
José Luis García Pallero |

**Subject**: |
In which functions is used the lapack DGELSY subroutine? |

**Date**: |
Thu, 26 Aug 2010 23:20:23 +0200 |

Hello,
Sorry for the stupid question, but I didn't find it in the Octave
source code. In which functions or operands (maybe '\'?) is used the
lapack routine DGELSY? I need it for a personal comparison against the
reference lapack compiled by myself. And another question, which is
the value by default used for RCOND argument of DGELSY in Octave?
I'm trying to solve an incomplete rank 'system' generated by rand()
function using the reference lapack 3.2.1 and 3.2.2 and I obtain
different results.
I made, for example
a=randn(1000,900);
and then, for make it rank deficient
a(:,901:905)=a(:,1:5)
Then I solve it with lapack DGELSY subroutine with RCOND=DLAMCH('P'),
that is the value of 'eps' in Octave. In Octave (linked against ATLAS
and lapack from the Debian repositories) I solve it as a\a (I suppose
that '\' calls DGELSY). The problem is that I obtain 3 different
solutions (lapack 3.2.1 and 3.2.2 computes differents ranks too).
Probably, the problem is the RCOND value, but I'm not sure. Or maybe
the randn() generated problem is not the correct way for test large
systems.
--
*****************************************
José Luis García Pallero
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Use Debian GNU/Linux and enjoy!
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**In which functions is used the lapack DGELSY subroutine?**,
*José Luis García Pallero* **<=**