Symmetric Drawings of Series Parallel Digraphs

The problem of drawing a graph symmetrically, however,
is NP-complete. For some special classes of graphs,
a symmetric drawing can be found in polynomial time.
In this talk we present an algorithm for drawing series
parallel digraphs with as much symmetry as possible.
The algorithm has two phases: the first phase computes
``geometric automorphisms'', that is, automorphisms of
the graph that can be represented as symmetries in the plane.
The second phase is an algorithm which draws the graph
to display these automorphisms.