  Network models facilitate inexpensive simulations, but require careful
handling of bifurcation conditions. We here present the graphnics library,
which combines FEniCS with NetworkX to facilitate network simulations using the
finite element method. Graphnics features (i) a FenicsGraph class built on top
of the NetworkX DiGraph class, that constructs a global mesh for a network and
provides FEniCS mesh functions describing how they relate to the graph
structure. (ii) Example models showing how the FenicsGraph class can be used to
assemble and solve different network flow models. (iii) Demos showing e.g. how
to run simulations on complex biological networks. Interestingly, the results
show that vasomotion modelled as a travelling sinusoidal wave is capable of
driving net perivascular fluid flow through an arterial tree, as has been
proposed based on experimental data.
