Is Minimax Linkage a Lance-Williams hierarchical clustering?












5












$begingroup$


I found the following article on "Hierarchical Clustering With Prototypes
via Minimax Linkage".



It is stated in Property 6 that




Minimax linkage cannot be written using Lance–Williams updates.




A succinct proof using a counter-example is given:




Proof.
Figure 9 shows a simple one-dimensional example that could not
arise if minimax linkage followed Lance– Williams updates. The upper
and lower panels show two configurations of points for which the
right side of (4) is identical but the left side differs; in
particular, $d(G_1 cup G_2,H) = 9$ for the upper panel, whereas
$d(G_1 cup G_2,H) = 8$ for the lower panel.




But I do not understand their proof. For both cases (upper and lower panels), $d(G_1,H) = 16$, $d(G_2,H) = 7$, $d(G_1,G_2) = 5$.



I cannot see any reason that $alpha(G_2)$ in the first case must equal $alpha(G_2)$ in the second case. For instance, $G_2$ has not the same cardinal.










share|improve this question











$endgroup$

















    5












    $begingroup$


    I found the following article on "Hierarchical Clustering With Prototypes
    via Minimax Linkage".



    It is stated in Property 6 that




    Minimax linkage cannot be written using Lance–Williams updates.




    A succinct proof using a counter-example is given:




    Proof.
    Figure 9 shows a simple one-dimensional example that could not
    arise if minimax linkage followed Lance– Williams updates. The upper
    and lower panels show two configurations of points for which the
    right side of (4) is identical but the left side differs; in
    particular, $d(G_1 cup G_2,H) = 9$ for the upper panel, whereas
    $d(G_1 cup G_2,H) = 8$ for the lower panel.




    But I do not understand their proof. For both cases (upper and lower panels), $d(G_1,H) = 16$, $d(G_2,H) = 7$, $d(G_1,G_2) = 5$.



    I cannot see any reason that $alpha(G_2)$ in the first case must equal $alpha(G_2)$ in the second case. For instance, $G_2$ has not the same cardinal.










    share|improve this question











    $endgroup$















      5












      5








      5


      1



      $begingroup$


      I found the following article on "Hierarchical Clustering With Prototypes
      via Minimax Linkage".



      It is stated in Property 6 that




      Minimax linkage cannot be written using Lance–Williams updates.




      A succinct proof using a counter-example is given:




      Proof.
      Figure 9 shows a simple one-dimensional example that could not
      arise if minimax linkage followed Lance– Williams updates. The upper
      and lower panels show two configurations of points for which the
      right side of (4) is identical but the left side differs; in
      particular, $d(G_1 cup G_2,H) = 9$ for the upper panel, whereas
      $d(G_1 cup G_2,H) = 8$ for the lower panel.




      But I do not understand their proof. For both cases (upper and lower panels), $d(G_1,H) = 16$, $d(G_2,H) = 7$, $d(G_1,G_2) = 5$.



      I cannot see any reason that $alpha(G_2)$ in the first case must equal $alpha(G_2)$ in the second case. For instance, $G_2$ has not the same cardinal.










      share|improve this question











      $endgroup$




      I found the following article on "Hierarchical Clustering With Prototypes
      via Minimax Linkage".



      It is stated in Property 6 that




      Minimax linkage cannot be written using Lance–Williams updates.




      A succinct proof using a counter-example is given:




      Proof.
      Figure 9 shows a simple one-dimensional example that could not
      arise if minimax linkage followed Lance– Williams updates. The upper
      and lower panels show two configurations of points for which the
      right side of (4) is identical but the left side differs; in
      particular, $d(G_1 cup G_2,H) = 9$ for the upper panel, whereas
      $d(G_1 cup G_2,H) = 8$ for the lower panel.




      But I do not understand their proof. For both cases (upper and lower panels), $d(G_1,H) = 16$, $d(G_2,H) = 7$, $d(G_1,G_2) = 5$.



      I cannot see any reason that $alpha(G_2)$ in the first case must equal $alpha(G_2)$ in the second case. For instance, $G_2$ has not the same cardinal.







      machine-learning clustering algorithms






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      edited 13 mins ago









      Chaitanya Bapat

      1318




      1318










      asked Sep 2 '15 at 13:34









      micmic

      298213




      298213






















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