No tree-walk, only P-P interactions.

examples/ZeldovichPancake_3D/makeIC.py

examples/ZeldovichPancake_3D/zeldovichPancake.yml

src/engine.c

src/gravity/Default/gravity_iact.h

src/gravity_cache.h

src/kernel_long_gravity.h

src/multipole.h

src/runner_doiact_fft.c

src/runner_doiact_grav.h