code: def _verify_barycentric(lambda1, lambda2, lambda3):
          
          weights_total = lambda1 + lambda2 + lambda3
          if not np.allclose(weights_total, 1.0, atol=0.0):
              raise ValueError(
                  "Weights do not sum to 1", lambda1, lambda2, lambda3
              )
  
          if lambda1 < 0.0 or lambda2 < 0.0 or lambda3 < 0.0:
              raise ValueError(
                  "Weights must be positive", lambda1, lambda2, lambda3
              )
docs: Verifies that weights are barycentric and on the reference triangle.
  
          I.e., checks that they sum to one and are all non-negative.
  
          Args:
              lambda1 (float): Parameter along the reference triangle.
              lambda2 (float): Parameter along the reference triangle.
              lambda3 (float): Parameter along the reference triangle.
  
          Raises:
              ValueError: If the weights are not valid barycentric
                  coordinates, i.e. they don't sum to ``1``.
              ValueError: If some weights are negative.