Fig. 4

Instantaneous speed of a travelling front for non-Gaussian threshold distributions. Measured front speed, extracted from a simulation of (3) (blue); theoretical value from (21) (red); and the threshold (4) (green) for a shifted exponential distribution (top) and a bump distribution (bottom) for \(\kappa=3\), \(h_{0}=0.3\) and \(L=50\). Equation (9) was truncated after 32 (top) and 64 (bottom) terms per sum, respectively. Other parameter values are \(\lambda=1\), \(\mu=-1\), \(\epsilon=-0.03\) (top) and \(A=\sqrt {2}\), \(B=2\), \(\alpha=0.5\), \(\epsilon=0.05\) (bottom)