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[Lapack] lapack bug in divide-and-conquer: is anybody listening

And sorry for also not getting to this sooner. When you say that the
convergence bug in divide-and-conquer was fixed by raising MAXIT
from 40 to 200 in xlaed4 (written by Ren-Cang), then that makes me
think that some flavor of bisection would be a better fall-back when
convergence fails (since the maximum number of iterations could be 
more like the number of bits in the floating point word, so 32 or 64).
This is very intricate code (and asking the to-be-hired programmer to fix
it would likely require a very long learning curve) so let me ask Ren-Cang
if he has any opinions.


julie langou wrote:
Sorry for not getting back to you earlier. 
We indeed corrected the bug you found, thank you for the patch. It is 
released in LAPACK 3.3.0 (released this week).
This bug was labelled bug0064.
If you could confirm that this issue is fixed, I will add a post on 
the forum to let the users know.

On Nov 18, 2010, at 8:25 AM, Evan Drumwright wrote:


Please allow me to say how much I use and appreciate lapack.  It 
makes my research *much* easier and I would be stuck without it.

... which is why the following problem is so disconcerting.  I am 
experiencing a bug related to least squares solution via singular 
value decomposition that at least one other person has experienced 
and have gotten no response on the lapack user's forum from the 
lapack maintainers.

Please see: 

for a description of the bug, conditions to reproduce it, and a fix. 
 I would greatly appreciate it if this fix made its way into lapack!

Thanks and regards,
Evan Drumwright

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Julie Langou; Research Associate in Computer Science
Innovative Computing Laboratory;
University of Tennessee from Denver, Colorado ;-)


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