Solving the Minimum Label Spanning Tree Problem by Mathematical Programming Techniques

Figure 7

LP solution of SCF_t with objective value 𝑓^lp=1+5/8(𝑙_𝑎=1/4,𝑙_𝑏=3/8,𝑙_𝑐=1). The blue arcs depict the flow variables with their according LP-values. Corresponding values for the edge variables are also shown. This solution is not valid for SCF_tn, as the sum over the set of labels adjacent to node 𝑣₂ is smaller than one.