  Consider a swarm of particles controlled by global inputs. This paper
presents algorithms for shaping such swarms in 2D using boundary walls. The
range of configurations created by conforming a swarm to a boundary wall is
limited. We describe the set of stable configurations of a swarm in two
canonical workspaces, a circle and a square. To increase the diversity of
configurations, we add boundary interaction to our model. We provide algorithms
using friction with walls to place two robots at arbitrary locations in a
rectangular workspace. Next, we extend this algorithm to place $n$ agents at
desired locations. We conclude with efficient techniques to control the
covariance of a swarm not possible without wall-friction. Simulations and
hardware implementations with 100 robots validate these results.
  These methods may have particular relevance for current micro- and
nano-robots controlled by global inputs.
