\HeaderA{Constants}{Built-in Constants}{Constants}
\aliasA{LETTERS}{Constants}{LETTERS}
\aliasA{letters}{Constants}{letters}
\aliasA{month.abb}{Constants}{month.abb}
\aliasA{month.name}{Constants}{month.name}
\aliasA{pi}{Constants}{pi}
\keyword{sysdata}{Constants}
\begin{Description}\relax
Constants built into \R.
\end{Description}
\begin{Usage}
\begin{verbatim}
LETTERS
letters
month.abb
month.name
pi
\end{verbatim}
\end{Usage}
\begin{Details}\relax
\R{} has a small number of built-in constants (there is also a rather
larger library of data sets which can be loaded with the function
\code{\LinkA{data}{data}}).

The following constants are available:
\Itemize{
\item \code{LETTERS}: the 26 upper-case letters of the Roman
alphabet;
\item \code{letters}: the 26 lower-case letters of the Roman
alphabet;
\item \code{month.abb}: the three-letter abbreviations for the
English month names;
\item \code{month.name}: the English names for the months of the
year;
\item \code{pi}: the ratio of the circumference of a circle to its
diameter.
}

These are implemented as variables in the base name space taking
appropriate values.
\end{Details}
\begin{References}\relax
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
\emph{The New S Language}.
Wadsworth \& Brooks/Cole.
\end{References}
\begin{SeeAlso}\relax
\code{\LinkA{data}{data}}, \code{\LinkA{DateTimeClasses}{DateTimeClasses}}.

\code{\LinkA{Quotes}{Quotes}} for the parsing of character constants,
\code{\LinkA{NumericConstants}{NumericConstants}} for numeric constants.
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
## John Machin (ca 1706) computed pi to over 100 decimal places
## using the Taylor series expansion of the second term of
pi - 4*(4*atan(1/5) - atan(1/239))

## months in English
month.name
## months in your current locale
format(ISOdate(2000, 1:12, 1), "%B")
format(ISOdate(2000, 1:12, 1), "%b")
\end{ExampleCode}
\end{Examples}

