\section{acos---Arc Cosine}
\label{fn:acos}
\index{acos()}
\index{arc cosine}
\index{inverse cosine}
\index{cosine!inverse}
\begin{rail}
ArcCosine : 'acos' '(' ( Scalar | Matrix ) ')' ;
\end{rail}

\verb+acos+ returns the arc cosine of the argument.  The return value
is expressed in radians, in the range $[ 0, \pi ]$. It is an error if the
magnitude of either the real or complex part of the argument exceeds
$1$.  If the argument is a matrix, then the operation is performed
element by element. 


\paragraph{Example}
\index{example of acos()}
\index{acos()!example}
\begin{verbatim}
> acos(1)
        0
> acos(0)
     1.57
> acos(-1)
     3.14
> acos(0.707+ 0.707j)
    0.999 - 0.764i
> c=0+1j
 c =
        0 + 1i
> acos(c)
     1.57 - 0.881i
> B = [ 0, -0.5 ; -0.3+1j, 0.4-0.003j]
 B =
                  0 + 0i               -0.5 + 0i
               -0.3 + 1i            0.4 - 0.003i
> acos(B)
               1.57 + 0i               2.09 + 0i
           1.78 - 0.897i         1.16 + 0.00327i
\end{verbatim}

See also: Page~\pageref{fn:acosh} \verb+acosh()+,
Page~\pageref{fn:asin} \verb+asin()+,
Page~\pageref{fn:atan} \verb+atan()+,
Page~\pageref{fn:atan2} \verb+atan2()+,
Page~\pageref{fn:cos} \verb+cos()+.

\newpage 



