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Derivative in left-hand-side #3838

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8439afe
Allow der-operator in the left-hand-side syntactically also for algor…
HansOlsson Feb 19, 2026
2f554ac
Also specify semantics of assignment to derivatives.
HansOlsson Feb 19, 2026
d5ff1c1
Based on feedback.
HansOlsson Mar 12, 2026
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28 changes: 6 additions & 22 deletions chapters/statements.tex
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Expand Up @@ -86,31 +86,15 @@ \section{Statements}\label{statements}
Names in a statement shall be found by looking up in the partially flattened enclosing class of the algorithm section.
\end{itemize}

The syntax of statements is as follows:
\begin{lstlisting}[language=grammar]
statement :
( component-reference ( ":=" expression | function-call-args )
| "(" output-expression-list ")" ":="
component-reference function-call-args
| break
| return
| if-statement
| for-statement
| while-statement
| when-statement
)
description
\end{lstlisting}
The syntax of statements is given by the production \lstinline[language=grammar]!statement! in \cref{equations1}.

\subsection{Simple Assignment Statements}\label{simple-assignment-statements}

The syntax of \firstuse[assignment statement!simple]{simple assignment statement} is as follows:
\begin{lstlisting}[language=grammar]
component-reference ":=" expression
\end{lstlisting}
A \firstuse[assignment statement!simple]{simple assignment statement} is an assignment statement where the left-hand side of the \lstinline!:=! is a component reference or a derivative.
The right-hand side of the \lstinline!:=! is evaluated, and the resulting value is stored into the left-hand side variable or derivative.

The \lstinline[language=grammar]!expression! is evaluated.
The resulting value is stored into the variable denoted by \lstinline[language=grammar]!component-reference!.
The resulting value is stored into the variable denoted by \lstinline[language=grammar]!component-reference! (or as its derivative).
An assignment to a derivative may only occur in a model or block.

The \lstinline!expression! must not have higher variability than the assigned component, see \cref{variability-of-expressions}.

Expand All @@ -119,7 +103,7 @@ \subsection{Simple Assignment Statements}\label{simple-assignment-statements}
\subsubsection{Assignments from Called Functions with Multiple Results}\label{assignments-from-called-functions-with-multiple-results}

There is a special form of assignment statement that is used only when the right-hand side contains a call to a function with multiple results.
The left-hand side contains a parenthesized, comma-separated list of variables receiving the results from the function call.
The left-hand side contains a parenthesized, comma-separated list of variables (or derivatives) receiving the results from the function call.
A function with $n$ results needs $m \leq n$ receiving variables on the left-hand side, and the variables are assigned from left to right.

\begin{lstlisting}[language=modelica]
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5 changes: 3 additions & 2 deletions chapters/syntax.tex
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Expand Up @@ -293,8 +293,9 @@ \subsection{Equations}\label{equations1}
description

statement-or-procedure :
component-reference ":=" expression
| component-reference function-call-args
component-reference function-call-args
| component-reference ":=" expression
| der "(" component-reference ")" ":=" expression

if-equation :
if expression then
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