I want to construct signal flow graphs using Mathematica. Below is a simple example. It works well enough except that it draws from right to left. In fact it seems to choose left to right or right to left in some mysterious way. I have been through all the Graph options and can't find one that will control this behavior.
What I really want is a linear left to right layout of the nodes, with any back-directed edges drawn above or below the linear layout
Any ideas?
Graph[{1 \[DirectedEdge] 2, 2 \[DirectedEdge] 3, 3 \[DirectedEdge] 4, 3 \[DirectedEdge] 2}, VertexLabels -> {1 -> "In", 2 -> "y1''", 3 -> "y1'", 4 -> "y1"}, EdgeLabels -> {2 \[DirectedEdge] 3 -> "1/s", 3 \[DirectedEdge] 4 -> "1/s", 3 \[DirectedEdge] 2 -> "-b/m"}] Produces

