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\title{Bad Box}

\author{SAM}

\maketitle


  For example
\begin{equation}
\bigtriangleup f = \frac{\partial^2 f}{\partial x^2} 
                 + \frac{\partial^2 f}{\partial y^2}
        \approx 
       \frac{f(x+h,y) + f(x-h,y) + f(x,y+h) + f(x,y-h) - 4}{h^2} \;\; .
\end{equation}
It is not necessary to approximate $\bigtriangleup f$ by approximating
the second partials separately in this way.  Another second order
accurate approximation is
\begin{displaymath}
\bigtriangleup f(x,y) \approx 
   \frac{f(x+h,y+h) + f(x+h,y-h) + f(x-h,y+h) + f(x-h,y-h) - 4f(x,y)}{2h^2}
                   \;\; .
\end{displaymath}

\end{document}