he quadratic models of the nonlinear equality functions at a
given point.

Parameters
----------
x : `numpy.ndarray`, shape (n,)
    Point at which to evaluate the quadratic models of the nonlinear
    equality functions.
mask : `numpy.ndarray`, shape (m_nonlinear_eq,), optional
    Mask of the quadratic models to consider.

Returns
-------
`numpy.ndarray`
    Values of the quadratic model of the nonlinear equality functions.
rz