This preprint was accepted October 26, 2003
ABSTRACT: The boundary control problem for the wave equation on a planar graph consisting of strings of variable densities with Dirichlet control at the boundary vertices is considered. The exact controllability in $L_2$-classes of controls and states is established in the case that the grapf is a tree; a sharp estimate of the time of controllability is given.[Full text: (.ps.gz)]