Formula to derive HPCG problem size - that fits in system memory about hpcg

[maherou]

Here is a rough formula for computing the memory usage:

You can get a rough estimate of data usage by knowing that the finest grid matrix
and related vectors use approximately for each MPI process:

27N - doubles, local ints, global ints (nonzero data for the sparse matrix)
N - size_t (pointer data for the sparse matrix)
7N - doubles (vectors used in the solution process)

Where N is the product of the local grid dimensions, specified as input to
the hpcg executable.

The size of local and global ints are compile-time parameters, but they
are commonly 4 bytes (int) and 8 bytes (long long), so we will assume that
size.

Then the sum is

27*( 8 + 4 + 8 )N +
8N +
78*N

Or 604N bytes per MPI process.

The coarse grids use a small fraction of the memory of the finest grid
(the reduction is a factor of 8 per level), so let's say the total memory
use by data objects is roughly 700N total bytes.

I hope this helps.