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\chapter{Mathematical expressions}
\label{mathtree}
At several points within \PyX{} mathematical expressions can be
provided in form of string parameters. They are evaluated by the
module \verb|mathtree|. This module is not described further in this
user manual, because it is considered to be a technical detail. We
just give a list of available operators, functions and predefined
variable names here.
\begin{description}
\item[Operators:]
\verb|+|; \verb|-|; \verb|*|; \verb|/|; \verb|**|
\item[Functions:]
\verb|neg| (negate); \verb|abs| (absolute value); \verb|sgn| (signum);
\verb|sqrt| (square root); \verb|exp|; \verb|log| (natural logarithm);
\verb|sin|, \verb|cos|, \verb|tan|, \verb|asin|, \verb|acos|,
\verb|atan| (trigonometric functions in radian units); \verb|sind|,
\verb|cosd|, \verb|tand|, \verb|asind|, \verb|acosd|, \verb|atand| (as
before but in degree units); \verb|norm| ($\sqrt{a^2+b^2}$ as an
example for functions with multiple arguments)
\item[predefined variables:]
\verb|pi| ($\pi$); \verb|e| ($e$)
\end{description}
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