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Derivative in left-hand-side #3838

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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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8 changes: 5 additions & 3 deletions chapters/statements.tex
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Expand Up @@ -90,6 +90,7 @@ \section{Statements}\label{statements}
\begin{lstlisting}[language=grammar]
statement :
( component-reference ( ":=" expression | function-call-args )
| der "(" component-reference ")" ":=" expression
| "(" output-expression-list ")" ":="
component-reference function-call-args
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@henrikt-ma henrikt-ma Mar 9, 2026 •
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Align with how it is written in the grammar, or take the opportunity to replace outdated duplicated grammar with cross reference to \cref{equations1}.

More generally, I would actually be in favor of making each production rule in syntax.tex its own listing, with a systematic way of creating a cross reference to a specific production rule with something like \cref{production:statement}. With precise cross references like that, the need to duplicate the production in other places of the document is more or less eliminated.

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@HansOlsson HansOlsson Mar 12, 2026

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I added the simple reference; a more precise cross-referencing would be good, but I think that should be a separate PR and prioritized.

| break
Expand All @@ -106,11 +107,12 @@ \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
( component-reference | der "(" component-reference ")" ) ":=" expression
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@henrikt-ma henrikt-ma Mar 9, 2026

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Without "repeating" the grammar:

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 restriction that \lstinline!der! is not allowed inside \lstinline!function! classes also applies to assignments.)
The right-hand side of the \lstinline!:=! is evaluated, and the resulting value is stored into the left-hand side variable or derivative.

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@HansOlsson HansOlsson Mar 12, 2026

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I copied that without the middle-line, and some update of the next paragraph (that already contained the restriction on derivatives.)

\end{lstlisting}

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 +121,7 @@ \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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1 change: 1 addition & 0 deletions chapters/syntax.tex
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Expand Up @@ -295,6 +295,7 @@ \subsection{Equations}\label{equations1}
statement-or-procedure :
component-reference ":=" expression
| component-reference function-call-args
| der "(" component-reference ")" ":=" expression

if-equation :
if expression then
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