This block delays the Boolean input by an infinitesimal time delay and therefore breaks algebraic loops. In a network of logical blocks, in every closed connection loop at least one logical block must have a delay because algebraic systems of Boolean equations are not practically solvable. The Pre block returns the value of the input signal from the last event iteration. Event iteration stops when both values are identical ($u=\mathrm{pre}\left(u\right)$).

$y=\mathrm{pre}\left(u\right)$

The component described in this topic is from the Modelica Standard Library. To view the original documentation, which includes author and copyright information, click here.