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.