[petsc-users] Creating and indexing large matrix with indexes exceeding the limit of the PetscInt

[Joon hee Choi]

Hello all,

I am setting up very large matrix(10^7 x 10^15) using MatCreateSeqAIJ and MatSetValues. However, in my computer, the maximum of PetscInt is about 4*10^9. So I cannot express the size and index of the matrix. By the way, I think I found a way from PETSC doc, and the doc is as follows:

* CHANGES in PETSc 2.2.1
- Introduced 4 new PETSc data types: PetscInt, PetscErrorCode, PetscMPIInt and PetscBLASInt. For 99% of users these are just int or integer*4 and you do not need to change your code.
- For users with more than roughly 2 billion unknowns you can run configure with --with-64-bit-ints and then PetscInt will represent 64 bit integers, long long int in C and integer*8 in Fortran. But the the other 3 types remain 32 bit (i.e. int in C and integer*4 in Fortran). Now you can index into vectors and matrices with virtually unlimited sizes.

However, I don't understand what this means exactly. How can I index into matrix with virtually unlimited sizes? Also, how can I use MatCreateSeqAIJ(MPI_Comm comm,PetscInt m,PetscInt n,PetscInt nz,const PetscInt nnz[],Mat *A) with n=10^15? If you know the solution of this, then let me know.

Thank you,

Joon