A refinement of an inequality of Johnson, Loewy and London on nonnegative matrices and some applications.
Let be a tree, let be its vertex. The branch weight of is the maximum number of vertices of a branch of at . The set of vertices of in which attains its minimum is the branch weight centroid of . For finite trees the present author proved that coincides with the median of , therefore it consists of one vertex or of two adjacent vertices. In this paper we show that for infinite countable trees the situation is quite different.
A theorem is proved which implies affirmative answers to the problems of E. Prisner. One problem is whether there are cycles of the line graph operator with period other than 1, the other whether there are cycles of the 4-edge graph operator with period greater than 2. Then a similar theorem follows.