docs: def _check_inputs(z, m):
      """Check inputs are arrays of same length or array and a scalar."""
      try:
          nz = len(z)
          z = np.array(z)
      except TypeError:
          z = np.array([z])
          nz = len(z)
      try:
          nm = len(m)
          m = np.array(m)
      except TypeError:
          m = np.array([m])
          nm = len(m)
  
      if (z < 0).any() or (m < 0).any():
          raise ValueError('z and m must be positive')
  
      if nz != nm and nz > 1 and nm > 1:
          raise ValueError('z and m arrays must be either equal in length, \
                            OR of different length with one of length 1.')
  
      else:
          if type(z) != np.ndarray:
              z = np.array(z)
          if type(m) != np.ndarray:
              m = np.array(m)
  
          return z, m