[rellumeister]

Hello,

Currently, I am investigating the possibility of optimizing a code. More prescisely, looking at the way OpenFOAM handles differential operators.

I took a tutorial case and clocked the time it took the solver to run over some differential operators at each timestep. I clocked fvm::laplacian(U) at the start of each timestep with the velocity field getting updated between timesteps. First, the fvm::laplacian(U) runs in roughly 110 tics, after which it drops down to a fifth (~20 tics) for the subsequent timesteps. After this, I added a fvm::div(phi,U) in the very beginning of the solver, right after the initialization of fields. By running the code again the tics were ~45 (divergence), ~85 (first laplacian) and ~20 (subsequent laplacians).


Something is clearly stored after the first differential operators which accounts for a shorter run time (data regarding the matrix?) However, by tracing the files, particularly fvmLaplacian, gaussLaplacianScheme and fmvDiv. However, I cannot understand what is going on...

So, essentially my question is what data is stored for future use when these are used the first time?

Br.
Ville