A golomb ruler is basicly a set of numbers where none of the 'distances' between each mark on the ruler are equal. This golomb ruler is just like a regular metric ruler, except the distances between each mark is different (which would make a rather awkward measurement tool :))
For example, a pretty easy golomb ruler set is 0, 1, 4, 9, and 11. The distance between 0 and 11 is not duplicated any where on the ruler. The distance between 1 and 4 (three) is not duplicated anywhere else on this particular ruler either, nor is the difference of 4 to 11 (note that I said 'difference,' as opposed to distance. The ruler part in 'Golomb Ruler' is just an analogy to a ruler, to make it a bit easier to understand during explanation). The point is, no where on the ruler are the distances between the marks equal.
The goal of a project such as OGR-24 (Optimal Golomb Ruler), is to find the golomb ruler with the least distance between each mark, but still to make sure that it stays golomb. The '24' in OGR-24 is the number of marks on each ruler. Obviously, this can become rather difficult to compute. Immagine how hard it would have been to even do an unoptimal 10 node golomb ruler with a pencil and paper (James Shearer maintains a list of the first 23 known optimal golomb rulers). Now, try to come up with a 24 mark optimal golomb ruler! It can get pretty intensive, as you can immagine, a perfect task for an internet based distributed computing project.
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