2d Simulation

I am a new Lammps user and was trying to understand the software.

I wanted to check whether while doing the 2d simulation LAMMPS is solving equations in all 3 dimensions with periodic boundary conditions in the 3rd direction or not. So I removed the fix enforce2d command in the flow example and dumped the velocity and force values in the 3rd direction onto a file. But, I was getting all the values as zeroes.
Its my understanding the enforce command initializes the force and velocity values to zero after every time step.

Thank You.

Everything you say is correct. The reason to use fix enforce2d
is to insure those values remain 0.0 forever. Since they
are computed in the code (e.g. in the pair style) there is no
guarantee they will remain exactly zero due to finite precision.