Weak scaling results of the PIC code measured in a strongly load-imbalanced simulation state. Scaling is presented in terms of the mean particle push time per processor for various simulations that have a fixed ratio of total number of particles to processors. The black line shows the total mean push time; the other curves show the individual results for each component in the loop (see Table 1). Ideal scaling corresponds to a horizontal line, although there is a slight increase in the evaluation time due to more time spent on communication routines as the number of processors increases.