plotting 3d discrete data



Let sol be a Maxima matrix. I'd like to plot the points [i * hx, j * ht, 
sol[i,j]],
where hx and ht are positive numbers (step sizes--for numerical methods 
class, I'm 
doing a finite difference method for the heat equation). I can do this via

  (%i89) f(x,t) := sol[round(x*nx),round(t * nt / t_final)];
  (%i90) plot3d(f(x,t),[x,0,1],[t,0,t_final]);

but it's slow. What is the better way?

Barton