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# scipy.cluster.hierarchy.cophenet

scipy.cluster.hierarchy.cophenet(Z, Y=None)

  Calculate the cophenetic distances between each observation in the hierarchical clustering defined by the linkage `Z`.

  Suppose `p` and `q` are original observations in disjoint clusters `s` and `t`, respectively and `s` and `t` are joined by a direct parent cluster `u`. The cophenetic distance between observations `i` and `j` is simply the distance between clusters `s` and `t`.

  Parameters:
    Z ndarray

      The hierarchical clustering encoded as an array (see `linkage` function).

    Y ndarray (optional)

      Calculates the cophenetic correlation coefficient `c` of a hierarchical clustering defined by the linkage matrix Z of a set of \(n\) observations in \(m\) dimensions. Y is the condensed distance matrix from which Z was generated.

  Returns:
    c ndarray

      The cophentic correlation distance (if `Y` is passed).

    d ndarray

      The cophenetic distance matrix in condensed form. The \(ij\) th entry is the cophenetic distance between original observations \(i\) and \(j\).

  See also

  `linkage`

    for a description of what a linkage matrix is.

  `scipy.spatial.distance.squareform`

    transforming condensed matrices into square ones.

  Examples

      >>> from scipy.cluster.hierarchy import single, cophenet
      >>> from scipy.spatial.distance import pdist, squareform

  Given a dataset `X` and a linkage matrix `Z`, the cophenetic distance between two points of `X` is the distance between the largest two distinct clusters that each of the points:

      >>> X = [[0, 0], [0, 1], [1, 0],
      ...      [0, 4], [0, 3], [1, 4],
      ...      [4, 0], [3, 0], [4, 1],
      ...      [4, 4], [3, 4], [4, 3]]

  `X` corresponds to this dataset

      x x    x x
      x        x

      x        x
      x x    x x

      >>> Z = single(pdist(X))
      >>> Z
      array([[ 0.,  1.,  1.,  2.],
             [ 2., 12.,  1.,  3.],
             [ 3.,  4.,  1.,  2.],
             [ 5., 14.,  1.,  3.],
             [ 6.,  7.,  1.,  2.],
             [ 8., 16.,  1.,  3.],
             [ 9., 10.,  1.,  2.],
             [11., 18.,  1.,  3.],
             [13., 15.,  2.,  6.],
             [17., 20.,  2.,  9.],
             [19., 21.,  2., 12.]])
      >>> cophenet(Z)
      array([1., 1., 2., 2., 2., 2., 2., 2., 2., 2., 2., 1., 2., 2., 2., 2., 2.,
             2., 2., 2., 2., 2., 2., 2., 2., 2., 2., 2., 2., 2., 1., 1., 2., 2.,
             2., 2., 2., 2., 1., 2., 2., 2., 2., 2., 2., 2., 2., 2., 2., 2., 2.,
             1., 1., 2., 2., 2., 1., 2., 2., 2., 2., 2., 2., 1., 1., 1.])

  The output of the `scipy.cluster.hierarchy.cophenet` method is represented in condensed form. We can use `scipy.spatial.distance.squareform` to see the output as a regular matrix (where each element `ij` denotes the cophenetic distance between each `i`, `j` pair of points in `X`):

      >>> squareform(cophenet(Z))
      array([[0., 1., 1., 2., 2., 2., 2., 2., 2., 2., 2., 2.],
             [1., 0., 1., 2., 2., 2., 2., 2., 2., 2., 2., 2.],
             [1., 1., 0., 2., 2., 2., 2., 2., 2., 2., 2., 2.],
             [2., 2., 2., 0., 1., 1., 2., 2., 2., 2., 2., 2.],
             [2., 2., 2., 1., 0., 1., 2., 2., 2., 2., 2., 2.],
             [2., 2., 2., 1., 1., 0., 2., 2., 2., 2., 2., 2.],
             [2., 2., 2., 2., 2., 2., 0., 1., 1., 2., 2., 2.],
             [2., 2., 2., 2., 2., 2., 1., 0., 1., 2., 2., 2.],
             [2., 2., 2., 2., 2., 2., 1., 1., 0., 2., 2., 2.],
             [2., 2., 2., 2., 2., 2., 2., 2., 2., 0., 1., 1.],
             [2., 2., 2., 2., 2., 2., 2., 2., 2., 1., 0., 1.],
             [2., 2., 2., 2., 2., 2., 2., 2., 2., 1., 1., 0.]])

  In this example, the cophenetic distance between points on `X` that are very close (i.e., in the same corner) is 1. For other pairs of points is 2, because the points will be located in clusters at different corners - thus, the distance between these clusters will be larger.