code: def hankel(c, r=None):
      """Construct a Hankel matrix.
  
      The Hankel matrix has constant anti-diagonals, with ``c`` as its first
      column and ``r`` as its last row. If ``r`` is not given, then
      ``r = zeros_like(c)`` is assumed.
  
      Args:
          c (cupy.ndarray): First column of the matrix. Whatever the actual shape
              of ``c``, it will be converted to a 1-D array.
          r (cupy.ndarray, optionnal): Last row of the matrix. If None,
              ``r = zeros_like(c)`` is assumed. ``r[0]`` is ignored; the last row
              of the returned matrix is ``[c[-1], r[1:]]``. Whatever the actual
              shape of ``r``, it will be converted to a 1-D array.
  
      Returns:
          cupy.ndarray: The Hankel matrix. Dtype is the same as
          ``(c[0] + r[0]).dtype``.
  
      .. seealso:: :func:`cupyx.scipy.linalg.toeplitz`
      .. seealso:: :func:`cupyx.scipy.linalg.circulant`
      .. seealso:: :func:`scipy.linalg.hankel`
      """
      c = c.ravel()
      r = cupy.zeros_like(c) if r is None else r.ravel()
      return _create_toeplitz_matrix(c, r[1:], True)
  
imports: import math
  import warnings
  import cupy
  from cupy import _core
  from cupyx.scipy.linalg import _uarray
label_desc: Use image node_id 6 for calling a global function with example usage: hankel(c, r) and returns: _create_toeplitz_matrix