  We consider initial-boundary value problems for the derivative nonlinear
Schr\"odinger (DNLS) equation on the half-line $x > 0$. In a previous work, we
showed that the solution $q(x,t)$ can be expressed in terms of the solution of
a Riemann-Hilbert problem with jump condition specified by the initial and
boundary values of $q(x,t)$. However, for a well-posed problem, only part of
the boundary values can be prescribed; the remaining boundary data cannot be
independently specified, but are determined by the so-called global relation.
In general, an effective solution of the problem therefore requires solving the
global relation. Here, we present the solution of the global relation in terms
of the solution of a system of nonlinear integral equations. This also provides
a construction of the Dirichlet-to-Neumann map for the DNLS equation on the
half-line.
