Sage Reference Manual: Numerical Optimization - Mirrors

Sage Reference Manual: Numerical Optimization, Release 6.1.1
•u – Name (as str) of the tail vertex
•v – Name (as str) of the head vertex
OUTPUT:
A triple describing if edge was found or None if not. The third value of the triple is a dict containing
the following edge parameters:
•low – The minimum flow through the edge
•cap – The maximum capacity of the edge
•cost – The cost of transporting one unit through the edge
•x – The actual flow through the edge after solving
EXAMPLE:
sage: from sage.numerical.backends.glpk_graph_backend import GLPKGraphBackend
sage: gbe = GLPKGraphBackend()
sage: edges = [("A", "B"), ("A", "C"), ("B", "C")]
sage: gbe.add_edges(edges)
sage: ed = gbe.get_edge("A", "B")
sage: print ed[0], ed[1], ed[2][’x’]
A B 0.0
sage: gbe.get_edge("A", "F") is None
True
get_vertex(vertex)
Returns a specific vertex as a dict Object.
INPUT:
•vertex – The vertex label as str.
OUTPUT:
The vertex as a dict object or None if the vertex does not exist. The dict contains the values used or
created by the different algorithms. The values associated with the keys following keys contain:
•“rhs” – The supply / demand value the vertex (mincost alg)
•“pi” – The node potential (mincost alg)
•“cut” – The cut flag of the vertex (maxflow alg)
•“es” – The earliest start of task (cpp alg)
•“ls” – The latest start of task (cpp alg)
EXAMPLE:
sage: from sage.numerical.backends.glpk_graph_backend import GLPKGraphBackend
sage: gbe = GLPKGraphBackend()
sage: verts = ["A", "B", "C", "D"]
sage: gbe.add_vertices(verts)
sage: sorted(gbe.get_vertex("A").items())
[(’cut’, 0), (’es’, 0.0), (’ls’, 0.0), (’pi’, 0.0), (’rhs’, 0.0)]
sage: gbe.get_vertex("F") is None
True
get_vertices(verts)
Returns a dictionary of the dictonaries associated to each vertex.
INPUT:
5.3. GLPK Backend for access to GLPK graph functions 87