[petsc-users] PetscInt overflow

[Zhang, Junchao]

On Fri, Oct 19, 2018 at 4:02 AM Jan Grießer <griesser.jan at googlemail.com<mailto:griesser.jan at googlemail.com>> wrote:
With more than 1 MPI process you mean i should use spectrum slicing in divide the full problem in smaller subproblems?
The --with-64-bit-indices is not a possibility for me since i configured petsc with mumps, which does not allow to use the 64-bit version (At least this was the error message when i tried to configure PETSc )

MUMPS 5.1.2 manual chapter 2.4.2 says it supports "Selective 64-bit integer feature" and "full 64-bit integer version" as well.

Am Mi., 17. Okt. 2018 um 18:24 Uhr schrieb Jose E. Roman <jroman at dsic.upv.es<mailto:jroman at dsic.upv.es>>:
To use BVVECS just add the command-line option -bv_type vecs
This causes to use a separate Vec for each column, instead of a single long Vec of size n*m. But it is considerably slower than the default.

Anyway, for such large problems you should consider using more than 1 MPI process. In that case the error may disappear because the local size is smaller than 768000.

Jose


> El 17 oct 2018, a las 17:58, Matthew Knepley <knepley at gmail.com<mailto:knepley at gmail.com>> escribió:
>
> On Wed, Oct 17, 2018 at 11:54 AM Jan Grießer <griesser.jan at googlemail.com<mailto:griesser.jan at googlemail.com>> wrote:
> Hi all,
> i am using slepc4py and petsc4py to solve for the smallest real eigenvalues and eigenvectors. For my test cases with a matrix A of the size 30k x 30k solving for the smallest soutions works quite well, but when i increase the dimension of my system to around A = 768000 x 768000 or 3 million x 3 million and ask for the smallest real 3000 (the number is increasing with increasing system size) eigenvalues and eigenvectors i get the output (for the 768000):
>  The product 4001 times 768000 overflows the size of PetscInt; consider reducing the number of columns, or use BVVECS instead
> i understand that the requested number of eigenvectors and eigenvalues is causing an overflow but i do not understand the solution of the problem which is stated in the error message. Can someone tell me what exactly BVVECS is and how i can use it? Or is there any other solution to my problem ?
>
> You can also reconfigure with 64-bit integers: --with-64-bit-indices
>
>   Thanks,
>
>     Matt
>
> Thank you very much in advance,
> Jan
>
>
>
> --
> What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
> -- Norbert Wiener
>
> https://www.cse.buffalo.edu/~knepley/

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