From: William James <w_a_x_man@...>
Date: 2006-12-21T11:55:07+09:00
Subject: Re: Common point puzzle

Bil Kleb wrote:
> Warning: the following really needs a sketch.
>
> I have a series of three (x,y) grids with values, z,
> at each point.  Each successive grid is twice as fine
> as the previous, i.e., dx1 = 2 * dx2 = 4 * dx3.
>
> For a series of three nested grids, I'd like to compute
> (z2-z1)/(z3-z2) at each of the points shared between all
> three grids, i.e., at all the points of the coarsest grid.
>
> The catch?  The (x,y) points are not ordered in the same
> fashion for each grid.  In other words, I need find the
> (x,y) coordinate shared by all three for each point in
> the coarsest grid.
>
> Now, I can do this with a bunch of conditional checks,
> but I thought it might be possible to use Ruby's set
> functions or Array intersection in some elegant way to
> create some sort of a mask that I could overlay the medium
> and fine grids with to find the coincident points.
>
> Thanks for reading this far,
> --
> Bil Kleb
> http://fun3d.larc.nasa.gov

What is the layout of the array?  Something like this?

[ [x1,y1,z1], [x2,y2,z2] ... ]