Landau constant $l_r$

In order to calculate the Landau constant, we should at first identify the transition regime and the the saturated regime, where the non-linear term $\frac{1}{2} l_r |A|^2 A$ dominates in the Landau equation. With the diagram of $A$ as function of $T A^2$, we can have the slope of the fitting line of these points. 

Figure 3.3 – Landau constant $l_r$ for $u^*=3.3$

For the case $u^*=3.3$ we have obtained that the Landau constant $l_r=-5.2<0$, which indicates a sub-critical regime, since here we have $u^*=3.3<u^*_{critical}$ ($u^*_{critical}=3.55$).