Fig. 3. Definition of a discrete variable x_max in a language with (Modelica) and without (Antimony) support for declaring discrete variables.

The variable x_max captures the peak value of the continuous variable x obtained within two seconds after an event event. a The Modelica model defines a discrete boolean variable in_window, to simplify the when condition later in the code. The information that this variable is discrete already lies in the type definition as Boolean. For real variables like x_max, there exists a keyword discrete, which determines that the variable value may only change within a when equation. b The same model structure and semantics can also be achieved in Antimony, but the discrete variables in_window and x_max each need an explicit rate rule to ensure that their value only changes when an event occurs (lines 3 and 8). Additionally, two events are needed to emulate the boolean variable in_window: One to update the value when the condition becomes true (line 4) and one to do so when it becomes false (line 5).