Is it true that the trackless workfunction on a cell is the minimum value
of the workfunction over all points in M which map to that cell?
Maybe not. In fact, the algorithm cannot know the actual values of the
workfunction w on the space M.
More Detailed Explanation
The algorithm may as well assume that M is a universal space.
If the algorithm remembers everything it can, it knows that the
true workfunction w lies within some set of possible workfunctions,
say W = {w_1, w_2, ... }
After t steps, the algorithm's knowledge of the past consists of a
partial distance function on pair of points drawn from the set
R = {s(0), r(0), r(1), .... r(t)}. That is the set of all points on
which the algorithm has had servers. That set has C(t+1,2) = (t^2+t)/2
pairs, but the algorithm knows only 2t distances. In principle, the
algorithm can compute the trackless work function as follows:
- Loop
- Choose a metric on R consistent with the algorithm's knowledge
- Using that metric, compute the values of the workfunction on R
- Project those values to the cells of the diagram.
- If all possible metrics have been chosen Exit
- End Loop
- For each cell, pick the minimum of all the projected values.
(Default value is infinity)
- For any cell(x,y), define f(x,y) to be the minimum of the quantity
value(e,f) + max{|x-e|,|y-f|}, minimized over all choices of cell(e,f)
which got a value in the previous step.
In practice, such a computation is far more complex than necessary, as
we shall see in the next lesson.