\subsection{Mehlum curvature of a B-spline or NURBS 
            surface as a NURBS surface.}
\funclabel{s2536}
\begin{minipg1}
To interpolate or approximate the Mehlum curvature of a B-spline or NURBS 
            surface by a NURBS surface. 
            The desired continuity of the Mehlum curvature surface is
            input and this may lead to a patchwork of output surfaces. 
            Interpolation results in a high order surface.
            If the original surface is a B-spline surface of order $k$,
            the result is of order $12k-17$, in the NURBS case,
            order $48k-53$.
            To avoid instability beacuse of this, a maximum order is
            applied. This may lead to an approximation rather than
            an interpolation.
\end{minipg1} \\ \\
SYNOPSIS\\
        \> void s2536(\begin{minipg3}
            {\fov surf}, {\fov u\_continuity}, {\fov v\_continuity}, {\fov u\_surfnumb}, 
	    {\fov v\_surfnumb}, {\fov mehlum\_surf}, {\fov stat})
                \end{minipg3}\\
                \>\>    SISLSurf \> *{\fov surf};\\
                \>\>    int    \>  {\fov u\_continuity};\\
                \>\>    int    \>  {\fov v\_continuity};\\
                \>\>    int    \>  *{\fov u\_surfnumb};\\
                \>\>    int    \>  *{\fov v\_surfnumb};\\
                \>\>    SISLSurf \> ***{\fov mehlum\_surf};\\
                \>\>    int    \>  *{\fov stat};\\
\\
ARGUMENTS\\
	\>Input Arguments:\\
        \>\>    {\fov surf}\> - \>  \begin{minipg2}
                     The original surface.
                               \end{minipg2}\\[0.8ex]
        \>\>    {\fov u\_continuity}\> - \>  \begin{minipg2}
                     Desired continuity of the Mehlum curvature surfaces
                          in the u direction: $0$ implies positional continuity,
                          $1$ implies tangential continuity, and so on.
                          SISL only accepts surfaces of continuity 0 or higher.
                          If the surface is to be intersected with another,
                          the continuity must be 1 or higher to find all the
                          intersection curves.
                               \end{minipg2}\\[0.8ex]
        \>\>    {\fov v\_continuity}\> - \>  \begin{minipg2}
                     Desired continuity of the Mehlum curvature surfaces
                          in the v direction: $0$ implies positional continuity,
                          $1$ implies tangential continuity, and so on.
                          SISL only accepts surfaces of continuity 0 or higher.
                          If the surface is to be intersected with another,
                          the continuity must be 1 or higher to find all the
                          intersection curves.
                               \end{minipg2}\\[0.8ex]
\\
	\>Output Arguments:\\
        \>\>    {\fov u\_surfnumb}\> - \>  \begin{minipg2}
                     Number of Mehlum curvature surface patches
                          in the u direction.
                               \end{minipg2}\\[0.8ex]
        \>\>    {\fov v\_surfnumb}\> - \>  \begin{minipg2}
                     Number of Mehlum curvature surface patches
                          in the v direction.
                               \end{minipg2}\\[0.8ex]
        \>\>    {\fov mehlum\_surf}\> - \>  \begin{minipg2}
                     The Mehlum curvature interpolation surfaces.
                          This will be a pointer to an array of length
                          {\fov u\_surfnum} * {\fov v\_surfnumb} of
                          SISLSurf pointers, where the indexing runs
                          fastest in the u direction.
                               \end{minipg2}\\[0.8ex]
        \>\>    {\fov stat}     \> - \> Status messages\\
                \>\>\>\>   $> 0$  \> : Warning.\\
                \>\>\>\>   $= 2$  \> : The surface is degenerate.\\
                \>\>\>\>   $= 0$  \> : Ok.\\
                \>\>\>\>   $< 0$  \> : Error.\\
\\
EXAMPLE OF USE\\
		\>      \{ \\

                \>\>    SISLSurf \> *{\fov surf};\\
                \>\>    int    \>  {\fov u\_continuity};\\
                \>\>    int    \>  {\fov v\_continuity};\\
                \>\>    int    \>  *{\fov u\_surfnumb};\\
                \>\>    int    \>  *{\fov v\_surfnumb};\\
                \>\>    SISLSurf \> ***{\fov mehlum\_surf};\\
                \>\>    int    \>  *{\fov stat};\\                \>\>    \ldots \\
        \>\>s2536(\begin{minipg4}
            {\fov surf},  {\fov u\_continuity},  {\fov v\_continuity},  {\fov u\_surfnumb}, 
	    {\fov v\_surfnumb}, {\fov mehlum\_surf}, {\fov stat});
                \end{minipg4}\\
                \>\>    \ldots \\
		\>      \}
\end{tabbing}
