\section{epsilon --- Compute machine epsilon}
\label{fn:epsilon}
\index{epsilon()}
\index{machine epsilon}
\begin{rail}
Epsilon : 'epsilon' '(' ')' ;
\end{rail}

\verb+epsilon+ calculates the epsilon of this machine.  Epsilon
is defined as the largest number you can add to $1$ and get a
result that is indiscernable from $1$.  There is a variable,
\verb+eps+, that is automatically placed into the global symbol table
by the default \verb+.rlab+ file.  You may find the variable more
convenient to use than the function, and the expense of possible
portablity problems.

$\Longrightarrow$ This is not an \RLaB\ built-in function.  This function
is normally loaded on start-up from the \verb+epsilon.r+ file in the
standard \verb+rlib+ directory. Use of the \verb+-r+ option, incorrectly 
setting the \verb+RLAB_LIB_DIR+ environmental variable, or modifying
\verb+epsilon.r+ may make this function unavailable.


\paragraph{Example}
\index{example of epsilon()}
\index{epsilon()!example}
\begin{verbatim}
> epsilon()
 1.11e-16
> eps
 eps =
 1.11e-16
> 1+epsilon()==1
        1
> 1+2*epsilon()==1
        0
\end{verbatim}

\newpage



