code: def cost_matrix(x, y, dist="square", region=None):
      """Compute the cost matrix between two samples.
  
      Parameters
      ----------
      x : array-like, shape = (n_timestamps_1,)
          First sample.
  
      y : array-like, shape = (n_timestamps_2,)
          Second sample.
  
      dist : 'square', 'absolute' or callable (default = 'square')
          Distance used. If 'square', the squared difference is used.
          If 'absolute', the absolute difference is used. If callable,
          it must be a function with a numba.njit() decorator that takes
          as input two numbers (two arguments) and returns a number.
  
      region : None or array-like, shape = (2, n_timestamps_1) (default = None)
          Constraint region. If None, there is no contraint region.
          If array-like, the first row indicates the starting indices (included)
          and the second row the ending indices (excluded) of the valid rows
          for each column.
  
      Returns
      -------
      cost_matrix : array, shape = (n_timestamps_1, n_timestamps_2)
          Cost matrix.
  
      """
      if dist == "square":
          dist_ = _square
      elif dist == "absolute":
          dist_ = _absolute
      elif isinstance(dist, str):
          raise ValueError(
              "'dist' must be either 'square', 'absolute' or "
              "callable (got {0}).".format(dist)
          )
      else:
          try:
              temp = dist(1, 1)
          except:  # noqa: E722
              raise ValueError("Calling dist(1, 1) did not work.")
          else:
              if not isinstance(temp, (int, float)):
                  raise ValueError(
                      "Calling dist(1, 1) did not return a float "
                      "or an integer."
                  )
          dist_ = dist
      if region is not None:
          region = check_array(region)
          region_shape = region.shape
          if region_shape != (2, x.size):
              raise ValueError(
                  "The shape of 'region' must be equal to (2, n_timestamps_1) "
                  "(got {0}).".format(region_shape)
              )
      if region is None:
          cost_mat = _cost_matrix_no_region(x, y, dist_)
      else:
          cost_mat = _cost_matrix_region(x, y, dist_, region)
      return cost_mat
  
imports: import numpy
  from math import ceil, log2, sqrt
  from numba import njit, prange
  from sklearn.utils import check_array
label_desc: Use image node_id 9 for calling a global function with example usage: cost_matrix(x, y, dist, region) and returns: cost_mat