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### [Lapack] diagonalization of a big matrix

 ``` 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/lapack-forum/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 32-bit 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 64-bit 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, 64-bit 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 ________________________________________________________________________________________________________________________________________________________ Veja quais s?o os assuntos do momento no Yahoo! + Buscados: Top 10 - Celebridades - M?sica - Esportes `````` ```
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