An 'upwa_plan_undi_graph' represents a plan_undi_graph with all directed edges and an associated upward representation. Such a representation is given by using two linear (left->right) lists of in/out-edges around each node. A necessary condition to make an upwa_plan_undi_graph object is that the graph used to initialize it has a candidate planar embedding (that is all in/out-edges around each node are consecutive).

When this condition is verified an upwa_plan_undi_graph upug is built, possibly adding a minimum number of switches (sources and sinks) on some edges. In this case, these dummy nodes (that we call "bends") are atumatically removed when passing upug to a draw_undi_graph object; drawings so obtained are called "quasi-upward drawings". An upward drawing is a quasi-upward drawing without bends.

Observe that this class is very similar to the orth_plan_undi one.

Three different kinds of 'bend_constraint' are possible for an edge:

Two different algorithms for producing a quasi-upward drawing upug: Both algorithms handle the bend constraints on edges.

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