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jodavies merged 1 commit into from
Dec 9, 2025
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doc: manual: add text on the interaction of extrasymbols and dummy indices #753

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25 changes: 24 additions & 1 deletion doc/manual/variable.tex
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Expand Up @@ -780,6 +780,28 @@ \section{Dummy indices}
found with which the above cases could be made to work without the penalty
in execution time, it will be built in in the future.

One must also take care when working with extra symbols when processing
expressions which contain dummy indices. Dummy indices which are inside
the extra symbol definitions are not visible to {\FORM}'s renumbering
routines, which can lead to ambiguous results. For example:
\begin{verbatim}
CFunction f,g;
Index mu;

Local test = f(mu,mu)*g(N1_?,N1_?);
ArgToExtraSymbol g;
Sum mu;
Argument g;
FromPolynomial;
EndArgument;

Print;
.end

test =
f(N1_?,N1_?)*g(N1_?,N1_?);
\end{verbatim}

\section{Kronecker delta's}

\label{sect-kroneckerdelta}
Expand Down Expand Up @@ -825,7 +847,8 @@ \section{Extra Symbols}
needed for some new manipulations and can also be very handy for output
that is to be treated by for instance a FORTRAN or C compiler. The
FromPolynomial statement replaces the extra symbols again by their original
meaning.
meaning. Care should be taken if extra symbol definitions include dummy
indices, see \ref{sect-dummies}.

% THIS EXAMPLE IS PART OF THE TESTSUITE. CHANGES HERE SHOULD BE APPLIED THERE AS
% WELL! (Var_Extra_Symbols_1)
Expand Down
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