  Force fluctuations in granular materials are investigated. A continuum
equation is derived starting from a discrete model proposed in the literature.
The influence of boundary conditions is investigated. For periodic boundary
conditions the average weight is found to increase linearly with depth while it
saturates to a constant value for absorbing boundary conditions, which models
the existence of walls. The scale dependencies of the saturation weight, the
saturation depth and the average squared fluctuations are obtained. The
analytical results are compared with previous works and with numerical
simulations in one dimension.
