code: def circos_radius(n_nodes, node_r):
      
      A = 2 * np.pi / n_nodes  # noqa
      B = (np.pi - A) / 2  # noqa
      a = 2 * node_r
      return a * np.sin(B) / np.sin(A)
docs: Automatically computes the origin-to-node centre radius of the Circos plot
      using the triangle equality sine rule.
  
      a / sin(A) = b / sin(B) = c / sin(C)
  
      :param n_nodes: the number of nodes in the plot.
      :type n_nodes: int
      :param node_r: the radius of each node.
      :type node_r: float
      :returns: Origin-to-node centre radius.