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

> with(plots):
> read data:
> surfdata(U,labels=[t,x,u],title=`g(x) = 1  using  nx = 20  and  nt = 30`);
> read data:
> surfdata(U,labels=[t,x,u],title=`g(x) = step functions  using  nx = 40  and  nt = 50`);
> surfdata(U,labels=[t,x,u],title=`Contour Plot`,style=PATCHCONTOUR, orientation=[90,0],axes=NORMAL,shading=ZHUE);
>