[petsc-users] mumps running out of memory, depending on an overall numerical factor?

[Jed Brown]

David Liu <daveliu at mit.edu> writes:

> Hi, I'm solving a 3d problem with mumps. When I increased the grid size to
> 70x60x20 with 6 unknowns per point, I started noticing that the program was
> crashing at runtime at the factoring stage, with the mumps error code:
>
> -17 The internal send buffer that was allocated dynamically by MUMPS on the
> processor is too small.
> The user should increase the value of ICNTL(14) before calling MUMPS again.
>
> However, when I increase the grid spacing in the z direction by about 50%,
> this crash does not happen.
>
> Why would how much memory an LU factorization uses depend on an overall
> numerical factor (for part of the matrix at least) like this?

I'm not sure exactly what you're asking, but the complexity of direct
solves depend on the minimal vertex separators in the sparse
matrix/graph.  Yours will be s=60*20*6 (more if your stencil needs
second neighbors).  The memory usage scales with s^2 and the
factorization time scales with s^3.
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