Dear Carolina,
Glad to hear that LAPACK served you well for six years.
I suspect N=20,000 (about) is the limit for our Divide and Conquer
interface unfortunately. This needs some more investigation. There is
a related post at:
https://icl.cs.utk.edu/lapackforum/viewtopic.php?f=2&t=1418
And this is bug report #0020 at
http://www.netlib.org/lapack/Errata/
If you do a worspace query (LWORK=1) what is the workspace needed? (
WORK(1) ). Is this value not above the integer overflow (2^31)? So that
when you feed it to the 32bit integer LWORK for the real run actually it
does not work. I do not quite get it. Because that should not be the case
for N=20,000.
Another possible problem is that it is not clear that WORK(1) (double
precision) convert correctly to LWORK (integer), you might be missing a
"one". If you do a workspace query can you try LWORK = LWORK + 1 (and
allocate with this plus one!).
I am positive that you can not use dpsevd for matrices bigger than 46,000
(sqrt(2^31)). LAPACK should be using 64bit integer for this.
(There is another limitation from packed format itself but it will hit us
later at N=2^16=65,536.)
Please keep in touch, to summarize, you can:
* check that the value LWORK before calling LAPACK "makes some sense" by
printing it
* add +1 to the LWORK before allocating the workspace
Yes, yes, 64bit integers in LAPACK ...
Best wishes,
Julien
On Sat, 13 Feb 2010, Carolina Brito wrote:
Hi!
I have been using CLAPACK in the past 6 years to diagonalize matrices up to
size 2000 x 2000 and I did not have any problem.
I am currently? using the routine? dspevd_()
I now want to diagonalize a matrix of size 20000 x 20000 and the routine
returns "segmentation fault".
I would like to know if there is a limit of size that this routine can
diagonalize of if this is a limitation of my computer (memory problems). This
is
important because I do not know if I should keep tying to use CLAPACK or if
it has some limitation that would not allow me to diagonalize such a big
matrix.
Thanks a lot.
carolina
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