# implicit block

Not to be confused with a Modelica block, an implicit block is a regular Activate block with an internal continuous-time state. The dynamics of an implicit block, unlike an explicit block, is defined in terms of a DAE (differential algebraic equation). Instead of the usual equation x’=f(t,x,u), the dynamics is defined by f(t,x’,x,u)=0. Implicit blocks can be used directly in Activate, but their main usage is for handling Modelica components which are grouped together and converted into a single implicit block after the pre-compilation phase.

Activate facilitates the use of implicit blocks for modeling physical systems. Implicit blocks have ports for defining constraints in a model, rather than the explicit inputs and outputs found in conventional physical component models.