The Event node () defines a solver event that can trigger the solver to stop, reinitialize some dependent variables, and then continue. For more information about solver events see The Events Interface in the COMSOL Multiphysics Reference Manual. The reinitialization step can either be defined by adding a Degree of Freedom Initialization node to the Event node, or adding a Degree of Freedom Re-Initialization node somewhere else.

To add this node, go to Building Blocks. Right-click Components to add a Component node. Then select Event from the Elements menu.

Enter a unique tag in the Event tag field to identify the event to Degree of Freedom Re-Initialization nodes. In the Event type list, choose the Explicit or Implicit event type. For explicit events, specify a Start time and optionally a Period for cyclic events. The implicit event requires a Condition that triggers the event when the value of the condition goes from 0 to 1. The condition must contain a degree of freedom with the Solver field type set to Quadrature in the Advanced section of either a Variable Definition node or a Dependent Variable Definition node. Note that this option is currently only supported for global states. Set the Solver field type to Discrete for global states that are discontinuous in time. Such states are typically used as logical help variables in if-statements to turn on and off equations.

You can choose Consistent initialization (1), From expression, or None (0) from the Initialization method list.