Positivity results are derived for explicit two-step methods formulated in linear multistep form and in one-leg form. It turns out that the latter formulation allows a slightly larger step size with respect to positivity

CWI
Modelling, Analysis and Simulation [MAS]
Computational Dynamics

Pham Thi, N., Hundsdorfer, W., & Sommeijer, B. (2005). Positivity for explicit two-step methods in linear multistep and one-leg form. Modelling, Analysis and Simulation [MAS]. CWI.