<｜begin▁of▁sentence｜>### Instruction:
As an emergency medical responder, imagine you're tasked with efficiently navigating through a complex series of roads to reach patients in need. Now, consider this: Given a map of these roads, some of which connect in one direction only, could you employ a specialized routing algorithm to plot the optimal path that minimizes intersections and highlights the hierarchical organization of these routes? This algorithm, akin to the Sugiyama layout in networkx, is implemented in the routing assistance feature of the GPS navigation system.
### Response:
import igraph as ig

# Create a directed acyclic graph (DAG)
g = ig.Graph.Directed(len(nodes))
edges = [(0, 1), (0, 2), (1, 3), (2, 3)]
nodes = ['a', 'b', 'c', 'd']
g.add_edges(edges)

# Run the Sugiyama layout algorithm
g.vs['name'] = nodes
layout, extended_graph = g.layout_sugiyama(return_extended_graph=True)

# Plot the graph with the Sugiyama layout
ig.plot(extended_graph, layout=layout, target='sugiyama_layout.png', bbox=(300, 300), margin=20)
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