In mathematics, a bi-directional delay line is a numerical analysis technique used in computer simulation for solving ordinary differential equations by converting them to hyperbolic equations.
In this way an explicit solution scheme is obtained with highly robust numerical properties.
It originates from simulation of hydraulic pipelines where wave propagation was studied.
It is used in the HOPSAN simulation package (Krus et al. 1990).
It is also known as the Transmission Line Modelling (TLM) from an independent development by Johns and O'Brian 1980.