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Using Matrices to Rank Teams
The table on the next page gives the records of all four teams in a soccer league. An entry of I indicates that the row team has defeated the column team. (There are no ties.) The teams are ranked, not by their percentage of victories, but by the number of points received under a ranking scheme that gives a team credit for the quality of the team it defeats. Since team A defeated B and C. A gels two points. Since B defeated C and D, and C defeated D, A gels 3 more secondarypoints for a total of 5 points.
(continued)
Since D's only victory is over A, D gels 1 point for that victory plus 2 secondary points for A‘s defeats of H and C. giving D a total of 3 points.
a) Write the table as a 4 X 4 matrix M and find M2.
b) Explain what the entries of M2 represent.
c) Now let T be a 4 X 1 matrix with a I in every entry. Find (M + M2)T.
d) Explain what the entries of (M + M2)T represent.
e) Is it possible for one team to have a better win-loss record than another, but end up ranked lower than the other because of this point scheme? Give an example to support your answer.
f) Make up a win-loss table (with no ties) for a six-team soccer league like the given table. Use a graphing calculator to find (M + M2)T. Compare the percentage of games won by each team with its ranking by this scheme. Is it possible for a team to have a higher percentage of wins but still be ranked lower than another team?
g) Find (2M + M2)T for the matrix M from part (0 and explain its entries. What is the significance of the number 2?
h) Compare the ranking of the six teams using (2M + M2)T and (M + M2)T. Is it possible that (2M + M2)T could change the order of the teams?
A |
B |
c |
D |
|
A |
0 |
1 |
1 |
0 |
B |
0 |
0 |
1 |
1 |
c |
0 |
0 |
0 |
1 |
D |
1 |
0 |
0 |
0 |

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