Maple session used to produce  surface plots for solution of Laplace's equation
   from data generated using finite difference method

> with(plots):
> read data:
> surfdata(U,labels=[x,y,u],title=`Example 1`);
> surfdata(U,labels=[x,y,u],style=PATCHCONTOUR, orientation=[90,0],axes=NORMAL,shading=ZHUE);
>