The tri-diagonal solvers used for computing the derivatives in Xcompact3d do not currently vectorise
well, particularly in the x-direction.
To test improvements to the Xcompact3d code, x3div extracts a simplified timestep based on the
Euler equations, including solution of the Poisson equation using 2decomp&fft.
Building the code requires a working mpi installation, depending on your compilers build using
make CMP=${compiler}
where ${compiler} is one of intel, gcc, cray or nagfor.
Running the produced binary will run the default benchmark for 5 seconds on a 16x16x16 grid, the
run can be customised on the commandline as:
mpirun -n ${N} xcompact3d $nx $ny $nz $prow $pcol $rt $test
where $nx, $ny, $nz specify the grid size, $prow <= $pcol, $prow * $pcol = $N specifies
parallel decomposition, $rt specifies how many seconds to run the benchmark for - note the
total time will be greater than this - and $test enables or disables computing the error in the
derivatives.
Each variable has a default value:
nx = ny = nz = 16
prow = pcol = 0
rt = 5
test = 0
setting $prow=$pcol=0 the code will attempt to determine a "good" parallel decomposition, $rt
must be an integer number of seconds and $test is an integer with zero interpreted as logical
false and any other value as true.
For benchmarking $test mode should be disabled, its intention is to validate custom
implementations of the compact finite difference scheme solvers.
Note this code is a very stripped down version of Xcompact3d, it is intended for profiling only.