Fig. 2.

Establishment of a target patter in a more realistic setting, in which a slowly varying heterogeneity was added to the control parameter A (for details, see SI Text). Results of the numerical solution of Eq. 1 (see Fig. 1 for more explanation) with the same parameters as in Fig. 1 (except for A), with uniform initial conditions are shown. The system is discretized by finite difference on a 400 × 400 grid, with reflecting boundary conditions. Initially, multiple nucleation events occur, leading to the formation of many competing wave sources, oscillating nearly in synchrony. Because of the presence of the heterogeneity, some of the sources have higher frequency, so after several periods the source with the highest frequency entrains other sources and takes over the whole system. Note the increased regularity of the observed wave pattern.