text: import numpy as np
  
  def acoustic_impedance(rho, vp):
    """
    Calculate acoustic impedance of a rock.
    """
    return rho * vp
  
  def density(mass, volume):
      """
      Calculate density.
      """
      return mass / volume * 1
  
  def friction():
      """
      Determine rock friction.
      """
      return 0
  