\section{cosh --- Hyperbolic Cosine}
\label{fn:cosh}
\index{cosh()}
\index{hyperbolic cosine}
\index{cosine!hyperbolic}
\begin{rail}
Cosh : 'cosh' '(' ( Scalar | Matrix ) ')' ;
\end{rail}

\verb+cosh+ calculates the hyperbolic cosine of the argument, specified
in radians.  If the argument is a matrix, then the operation is 
performed element-by-element.

$\Longrightarrow$ This is not an \RLaB\ built-in function.  This function
is normally loaded on start-up from the \verb+cosh.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+cosh.r+ may make this function unavailable.

\paragraph{Example}
\index{example of cosh()}
\index{cosh()!example}
\begin{verbatim}
> cosh(0)
        1
> cosh(pi)
     11.6
> cosh(0+1j)
     0.54
> cosh(0+10j)
   -0.839
> cosh(pi/2)
     2.51
> a = rand(2,5)*4
 a =
        4       2.59      0.148       2.66      0.817  
      3.9       1.33      0.647      0.339      0.669  
> cosh(a)
     27.3        6.7       1.01       7.17       1.35  
     24.7       2.03       1.22       1.06       1.23 
\end{verbatim}

See also: Page~\pageref{fn:acosh} \verb+acosh()+,
Page~\pageref{fn:asinh} \verb+asinh()+,
Page~\pageref{fn:atanh} \verb+atanh()+,
Page~\pageref{fn:cos} \verb+cos()+,
Page~\pageref{fn:exp} \verb+exp()+,
Page~\pageref{fn:sinh} \verb+sinh()+,
Page~\pageref{fn:tanh} \verb+tanh()+.

\newpage





