FIG. 8.

Color maps of $S_{vc}$ vs $\sigma$ and $\gamma$ in the amplitude equation (AE) model. (a) Purely random initial conditions of $\mathrm{\Delta }a$ and $\mathrm{\Delta }c$ (spatial scale $l=1$ cell). (b) Random initial conditions with a spatial scale of $l=20$ cells. $\alpha =0.5$ and $\rho =0.5$. Note that in the upper-left and lower-right quadrals, $\gamma \sigma <0$, the spatially discordant alternans (SDA) dynamics is quasiperiodic, $S_{vc}$ measured at the last beat depends on the status the SDA pattern, which varies from beat to beat. Therefore, the $S_{vc}$ values in these two quadrals exhibit a randomlike pattern in the color map. In the upper-right (electromechanically concordant) and lower-left (electromechanically discordant) quadrals, the SDA patterns are phase-locked and stable.