What is specific about equations in Modelica?
Equations are more powerful than assignments, since one equation can express several different assignments.
What is a declaration equation?
A declaration equation is the equation used when declaring a variable, usually constants or parameters. Such equations are actually required for constants, but are optional for parameters. It is also possible to specify a declaration equation for a normal state variable, but this will make the variable behave as a kind of constant.
What is a modifier equation?
Modifier equations occur for example in a variable declaration when there is a need to modify the default value of an attribute of the variable. A modifier equation replaces the declaration equation, if present, for an attribute of the specific type.