Explain why complete matching impossible

A question is this type if and only if it asks to explain or identify why a complete matching cannot be achieved in a given bipartite graph scenario.

3 questions · Moderate -0.8

7.02e Bipartite graphs: K_{m,n} notation7.04e Route inspection: Chinese postman, pairing odd nodes
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AQA D1 2013 January Q1
4 marks Moderate -0.8
1
  1. Draw a bipartite graph to represent the following adjacency matrix.
    12345
    A00001
    \(\boldsymbol { B }\)00011
    \(\boldsymbol { C }\)01011
    \(\boldsymbol { D }\)00011
    \(\boldsymbol { E }\)11101
  2. If \(A , B , C , D\) and \(E\) represent five people and 1, 2, 3, 4 and 5 represent five tasks to which they are to be assigned, explain why a complete matching is impossible.
    (2 marks)
Edexcel D1 Q3
11 marks Moderate -0.8
3. This question should be answered on the sheet provided. A firm of auditors is to place one trainee accountant at each of its five offices. These are situated in Dundee, Edinburgh, Glasgow and London. There are two offices in London, one of which is the company's Head Office. The table summarises the trainees' preferences.
TraineePreferences
\(P\)Dundee, London (either)
\(Q\)Dundee, Edinburgh, Glasgow
\(R\)Glasgow, London (Head Office only)
SEdinburgh
\(T\)Edinburgh
  1. Draw a bipartite graph to model this situation.
  2. Explain why no complete matching is possible. Trainee \(T\) is persuaded that either office in London would be just as good for her personal development as the Edinburgh office.
  3. Draw a second bipartite graph to model the changed situation. In an initial matching, trainee \(P\) is placed in the Dundee office, trainee \(R\) in the Glasgow office, and trainee \(S\) in the Edinburgh office.
  4. Draw this initial matching.
  5. Starting from this initial matching, use the maximum matching algorithm to find a complete matching. You must indicate how the algorithm has been applied, stating clearly the alternating paths you use and the final matching.
    (7 marks)
Edexcel D1 2014 June Q2
7 marks Moderate -0.8
2. \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{23cc3c59-35d8-4120-9965-952c0ced5b3d-3_437_399_251_511} \captionsetup{labelformat=empty} \caption{Figure 1}
\end{figure} \begin{figure}[h]
\includegraphics[alt={},max width=\textwidth]{23cc3c59-35d8-4120-9965-952c0ced5b3d-3_437_401_251_1151} \captionsetup{labelformat=empty} \caption{Figure 2}
\end{figure} Figure 1 shows the possible allocations of five employees, Ali (A), Campbell (C), Hugo (H), Janelle (J) and Polly (P), to five tasks 1, 2, 3, 4 and 5.
  1. Explain why it is not possible to find a complete matching. It is decided that one of the employees should be trained so that a complete matching becomes possible. There are only enough funds for one employee to be trained. Two employees volunteer to undergo training. Janelle can be trained to do task 1 or Hugo can be trained to do task 5.
  2. Decide which employee, Janelle or Hugo, should undergo training. Give a reason for your answer. You may now assume that the employee you identified in (b) has successfully undergone training. Figure 2 shows an initial matching.
  3. Starting from the given initial matching, use the maximum matching algorithm to find a complete matching. You should list the alternating path that you use, and state the complete matching.