Merge pull request #2960 from henrikt-ma/cleanup/constant-declaration…

…-equation

Move and add reference to rule about constants having declaration equation

chapters/classes.tex

@@ -358,6 +358,10 @@ \subsection{Component Variability Prefixes discrete, parameter, constant}\label{
   not differentiable.
 \end{itemize}
 
+Components declared as \lstinline!constant! shall have an associated declaration equation with a constant expression, if the constant is directly in the simulation model, or used in the simulation model.
+The value of a constant can be modified after it has been given a value, unless the constant is declared \lstinline!final! or modified with a \lstinline!final! modifier.
+A constant without an associated declaration equation can be given one by using a modifier.
+
 If a \lstinline!Real! variable is declared with the prefix \lstinline!discrete!\indexinline{discrete} it must in a simulation model be assigned in a \lstinline!when!-clause, either by an assignment or an equation.
 The variable assigned in a \lstinline!when!-clause shall not be defined in a sub-component of \lstinline!model! or \lstinline!block! specialized class.
 (This is to keep the property of balanced models.)

chapters/equations.tex

@@ -722,6 +722,7 @@ \section{Events and Synchronization}\label{events-and-synchronization}
 verification already at compile time.
 \end{nonnormative}
 
+
 \section{Initialization, initial equation, and initial algorithm}\label{initialization-initial-equation-and-initial-algorithm}
 
 Before any operation is carried out with a Modelica model (e.g., simulation or linearization), initialization takes place to assign consistent values for all variables present in the model.
@@ -772,16 +773,17 @@ \section{Initialization, initial equation, and initial algorithm}\label{initiali
   Implicitly by using the \lstinline!start!-attribute for variables with \lstinline!fixed = true!.  With \lstinline!start! given by \lstinline!startExpression!:
   \begin{itemize}
   \item
-    For a non-discrete-time \lstinline!Real! variable \lstinline!vc!, the equation \lstinline!vc = startExpression! is added to the initialization equations.
+    For a variable declared as \lstinline!constant! or \lstinline!parameter!, no equation is added to the initialization equations.
   \item
     For a discrete-time variable \lstinline!vd!, the equation \lstinline!pre(vd) = startExpression! is added to the initialization equations.
   \item
-    For a variable declared as \lstinline!constant! or \lstinline!parameter!, no equation is added to the initialization equations.
+    For a non-discrete-time \lstinline!Real! variable \lstinline!vc!, the equation \lstinline!vc = startExpression! is added to the initialization equations.
   \end{itemize}
 \end{enumerate}
 
-For constants and parameters, the attribute \lstinline!fixed! defaults to \lstinline!true!, which is the only allowed value for a constant.  For other variables,
-\lstinline!fixed! defaults to \lstinline!false!.
+Constants shall be determined by declaration equations (see \cref{component-variability-prefixes-discrete-parameter-constant}), and \lstinline!fixed = false! is not allowed.
+For parameters, \lstinline!fixed! defaults to \lstinline!true!.
+For other variables, \lstinline!fixed! defaults to \lstinline!false!.
 
 \lstinline!start!-values of variables having \lstinline!fixed = false! can be used as initial guesses, in case iterative solvers are used in the initialization phase.
 

chapters/operatorsandexpressions.tex

@@ -1436,8 +1436,6 @@ \subsection{Constant Expressions}\label{constant-expressions}
   \end{itemize}
 \end{itemize}
 
-Components declared as \lstinline!constant! shall have an associated declaration equation with a constant expression, if the constant is directly in the simulation model, or used in the simulation model.  The value of a constant can be modified after it has been given a value, unless the constant is declared \lstinline!final! or modified with a \lstinline!final! modifier.  A constant without an associated declaration equation can be given one by using a modifier.
-
 \subsection{Parameter Expressions}\label{parameter-expressions}
 
 Parameter expressions\index{parameter expression}\index{expression variability!parameter}\index{parametric variability|see{parameter expression}} are: