code: def evaluate_cartesian(self, s, t, _verify=True):
          r
          if _verify:
              self._verify_cartesian(s, t)
          return _surface_helpers.evaluate_barycentric(
              self._nodes, self._degree, 1.0 - s - t, s, t
          )
docs: r"""Compute a point on the surface.
  
          Evaluates :math:`B\left(1 - s - t, s, t\right)` by calling
          :meth:`evaluate_barycentric`:
  
          This method acts as a (partial) inverse to :meth:`locate`.
  
          .. testsetup:: surface-cartesian
  
             import numpy as np
             import bezier
  
          .. doctest:: surface-cartesian
             :options: +NORMALIZE_WHITESPACE
  
             >>> nodes = np.asfortranarray([
             ...     [0.0, 0.5, 1.0  , 0.0, 0.5, 0.25],
             ...     [0.0, 0.5, 0.625, 0.5, 0.5, 1.0 ],
             ... ])
             >>> surface = bezier.Surface(nodes, degree=2)
             >>> point = surface.evaluate_cartesian(0.125, 0.375)
             >>> point
             array([[0.16015625],
                    [0.44726562]])
             >>> surface.evaluate_barycentric(0.5, 0.125, 0.375)
             array([[0.16015625],
                    [0.44726562]])
  
          Args:
              s (float): Parameter along the reference triangle.
              t (float): Parameter along the reference triangle.
              _verify (Optional[bool]): Indicates if the coordinates should be
                  verified inside of the reference triangle. Defaults to
                  :data:`True`.
  
          Returns:
              numpy.ndarray: The point on the surface (as a two dimensional
              NumPy array).