code: def _tm(self, theta, phi, psi, dx, dy, dz):
          
          matrix = self.get_matrix(theta, phi, psi, dx, dy, dz)
          coord = matrix.dot(self.coord2)
          dist = coord - self.coord1
  
          d_i2 = (dist * dist).sum(axis=0)
  
          tm = -(1 / (1 + (d_i2 / self.d02)))
  
          return tm
docs: Compute the minimisation target, not normalised.