In: Statistics and Probability
The blood vessels in a lung branch into ever smaller capillary
vessels to facilitate the exchange of oxygen with the blood carried
by the capillary vessels. One hypothesis is that the resulting form
of the branching maximizes the surface area covered by the vessels.
We can test this hypothesis with a very simple (and admittedly not
too realistic) model of a 'lung' in two dimensions. Consider a
blood vessel of unit length, which branches into two vessels each
of length f, with f < 1. The two smaller vessels are 120 degree
apart. Each of them then branches in the same way, with the new
branches reduced in length by the same factor f. Repeat this
process ad infinitum. We obtain then a fractal tree, which is
called the Golden Tree. For too small a reduction factor, say f =
0.5, for example, you will find that large gaps of space remain
that are not covered by the branches of the tree. With too large a
reduction factor, say f = 0.7, you will find that the branches
overlap.
Find the optimal f that yields an arrangement with the branches
just about to touch.