[petsc-users] Large MATMPIAIJ - 32bit integer overflow in nz value

[Barry Smith]

  Yeah, this is silly. The check is just a "sanity-check" on the data in the file. We store redundant information in the matrix header in the file, header[3] is the total number of nonzeros in the matrix. When nz is too large, the correct value cannot fit in the header.

  Changing the file format would be a breaking change meaning old files could no longer be read (MatLoad() can still load binary files saved in 1995) which would be bad.

  I think the easiest way to handle this is to provide an option to avoid the unneeded (and doesn't work) sanity check. In other words, something like -mat_load_ignore_nz turns off the sanity check in MatLoad_MPIAIJ_Binary(). Is that something you could try in an MR or would you prefer we do it?

  Barry




> On May 17, 2023, at 8:55 AM, Fleischli Benno HSLU T&A <benno.fleischli at hslu.ch> wrote:
> 
> Dear PETSc developers
> 
> I am creating a very large parallel sparse matrix (MATMPIAIJ) with PETSc. I write this matrix to disk.
> The number of non-zeros exceeds the maximum number a 32-bit integer can hold.
> When I read the matrix from disk i get an error because there was an overflow in the nz number.
> (see petsc-3.18.4/src/mat/impls/aij/seq/aij.c:4977)
> 
> Obviously I could compile PETSc with 64bit integers (--with-64-bit-indices).
> But I wanted to ask if there is another way. Because the total number of nonzeros nz is the only numer that exceeds the 32bit limit.
> It would not be efficient to use 64bit integers everywhere just because of this single number.
> 
> This how I configured PETSc:
> 
> ./configure --download-fblaslapack --download-hpddm --download-hypre --with-debugging=0 
> COPTFLAGS='-O3 -march=native -mtune=native' CXXOPTFLAGS='-O3 -march=native -mtune=native' 
> FOPTFLAGS='-O3 -march=native -mtune=native' --with-scalar-type=real (--with-mpi-dir=/home/benno/Libraries/openMPI)
> 
> 
> 
> Kind Regards
> 
> Benno
> 
> 
> 
> ________________________________
> Hochschule Luzern
> Technik & Architektur
> Institute for Mechanical Engineering and Energy Technology
> Competence Center Fluid Mechanics and Numerical Methods
> 
> Benno Fleischli
> MSc in Mechanical Engineering / BSc in Electrical Engineering
> Wissenschaftlicher Mitarbeiter
> benno.fleischli at hslu.ch <https://webmail.hslu.ch/owa/redir.aspx?C=rM5K5xPd_kKJmyojcJXaG18BaXM9wM8IqSslYJQen5H6HtdiNS2KtWNFL89yfRdRtW-Oa6xCXTk.&URL=mailto%3akatrina.kemp%40hslu.ch>
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