strengths $D_{ij}$ and $S_{ij}$ at site $(i,j)$ are interpreted as number of $D$- and $S$-particles, respectively, present at that site. The two fields determine the transition probability in such a way that a particle movement in the direction of higher fields becomes more likely.

The dynamic floor field $D$ represents a virtual trace left by [*moving*]{} pedestrians. Similar to the process of chemotaxis [@chemo; @ants] used by some insects for communication, this trace has its own dynamics, namely diffusion and decay. Two parameters, $\alpha$ $\in[0,1]$ and $\delta$ $\in[0,1]$, control the broadening and dilution of the trace. Every moving pedestrian creates a $D$-particle at its origin cell. Since there is no restriction of the maximal number of $D$-particles at a site, $D$ can be regarded as a [*bosonic field*]{}.

The static floor field $S$, on the other hand, does not change in time. It reflects the surrounding geometry and e.g. specifying attractive space regions. In the case of the evacuation processes considered here, the static floor field describes the shortest distance to an exit door. $S$ is calculated for each lattice site using some distance metric. The field value increases in the direction of the exit such that it is largest 