visibility part of sort and conquer algorithm proposed by Ghosh et al

blog_vg_wvisibility.py

def wvisibility(x, left, right, i, graph):
  '''Weighted visibility module of sort and conquer algorithm proposed by Ghosh et al.
  
  Parameters:
    x: numpy.array
      A 1d time series.
    left: int
      Leftmost node connected to current node.
    right: int
      Rightmost node connected to current node.
    i: int
      Current node.
    graph: scipy.sparse.lil.lil_matrix
      A graph in row-based list of lists format.
  '''
  max_slope = float('-inf')
  min_slope = float('+inf')
  for j in np.arange(i + 1, right):
    slope = (x[j] - x[i]) / (j - i)
    if slope > max_slope:
      max_slope = slope
      graph[i, j] = np.arctan(slope)
      graph[j, i] = np.arctan(slope)
  for j in np.arange(i - 1, left, -1):
    slope = (x[i] - x[j]) / (i - j)
    if slope < min_slope:
      min_slope = slope
      graph[i, j] = np.arctan(slope)
      graph[j, i] = np.arctan(slope)