If it’s unclear, you can also check the book, operations Research: An introduction , 8th edition by Hamdy. A . Taha. From page 240- 242

Example 6.2-1 1 Midwest TV Cable Company is in the process of providing cable service to five new housing development areas. Figure 6.6 depicts possible TV linkages among the five areas. The cable miles are shown on each arc. Determine the most economical cable network. The algorithm starts at node 1 (any other node will do as well), which gives C = {1}, C = {2, 3, 4, 5, 6} The iterations of the algorithm are summarized in Figure 6.7. The thin arcs provide all the candi- date links between C and C. The thick branches represent the permanent links between the nodes of the connected set C, and the dashed branch represents the new (permanent) link added at each iteration. For example, in iteration 1, branch (1, 2) is the shortest link (= 1 mile) among all the candidate branches from node 1 to nodes 2, 3, 4, 5, and 6 of the unconnected set C. Hence, link (1,2) is made permanent and j = 2, which yields C=(1,2), (3,4,5,6) The solution is given by the minimal spanning tree shown in iteration 6 of Figure 6.7. The resulting minimum cable miles needed to provide the desired cable service are 1+3+ 4+3+5= 16 miles. TORA Moment You can use TORA to generate the iterations of the minimal spanning tree. From Main menu, select Network models Minimal spanning tree. Next, from SOLVE/ MODIFY menu, select Solve problem Go to output screen. In the output screen, select a Starting node then use Next iteration or All iterations to generate the succes- sive iterations. You can restart the iterations by selecting a new Starting Node. File toraEx6.2-1.txt gives TORA's data for Example 6.2-1. 242 Chapter 6 Network Models SE 1100 LA 1300 2000 FIGURE 6.8 Network for Problem 3, Set 6.2a (DE) 2600 1400 2000 1000 780 900 2 9 (CH) Iteration 1 1300 3 Iteration 3 Iteration 5 E 6.7 on iterations for Midwest TV Company 800 2 10 ww 200 DO 5 (NY) 5 C 6.2 Minimal Spanning Tree Algorithm 241 S 3 Iteration 2 Iteration 4 LEM SET 6.2A Solve Example 6.2-1 starting at node 5 (instead of node 1), and show that the algorithm produces the same solution. 3 Determine the minimal spanning tree of the network of Example 6.2-1 under each of the following separate conditions: (a) Nodes 5 and 6 are linked by a 2-mile cable. (b) Nodes 2 and 5 cannot be linked. (c) Nodes 2 and 6 are linked by a 4-mile cable. 3 Iteration 6 (Minimal spanning tree) Alternate links 5 C (d) The cable between nodes 1 and 2 is 8 miles long. (e) Nodes 3 and 5 are linked by a 2-mile cable. (f) Node 2 cannot be linked directly to nodes 3 and 5. 3. In intermodal transportation, loaded truck trailers are shipped between railroad terminals on special flatbed carts. Figure 6.8 shows the location of the main railroad terminals in the United States and the existing railroad tracks. The objective is to decide which tracks should be "revitalized" to handle the intermodal traffic. In particular, the Los Angeles (LA) terminal must be linked directly to Chicago (CH) to accommodate expected heavy traffic. Other than that, all the remaining terminals can be linked, directly or indirectly, such that the total length (in miles) of the selected tracks is minimized. Determine the seg- ments of the railroad tracks that must be included in the revitalization program. 4. Figure 6.9 gives the mileage of the feasible links connecting nine offshore natural gas wellheads with an inshore delivery point. Because wellhead 1 is the closest to shore, it is equipped with sufficient pumping and storage capacity to pump the output of the remain- ing eight wells to the delivery point. Determine the minimum pipeline network that links the wellheads to the delivery point.