For
let
be a one-dimensional Brownian motion on the interval
with absorption at the endpoints. At each instant in time, one must decide to run some subset of these d Brownian motions while holding the others fixed at their current state. The resulting process evolves in the rectangle
. If, at some instant, one decides to freeze all of the Brownian motions, then a reward is received in accordance with this final position. Two types of reward functions are considered. First, it is assumed that the reward is zero everywhere in D, except along the d edges that correspond to the coordinate axes. Along these edges, it is given by
strictly concave functions
, which are zero at the endpoints 0 and
of their domains. The optimal control for this problem has a simple description. Let
and put
. It is proved that the optimal control is: On
run any Brownian motion except the ith and stop the first time an edge is reached. The second class of reward functions are assumed to be zero everywhere except on the facets of D that meet at the origin. On the
such facet (i.e., where
), the reward function is the product of
for
. Put
. The optimal control is: On
run the
Brownian motion and stop when a facet of D is reached.