双1次曲面
∂ N 0 ∂ v = − 1 4 ( 1 − u ) {\displaystyle {\frac {\partial N_{0}}{\partial v}}=-{1 \over 4}(1-u)}
∂ N 1 ∂ v = − 1 4 ( 1 + u ) {\displaystyle {\frac {\partial N_{1}}{\partial v}}=-{1 \over 4}(1+u)}
∂ N 2 ∂ v = 1 4 ( 1 + u ) {\displaystyle {\frac {\partial N_{2}}{\partial v}}={1 \over 4}(1+u)}
∂ N 3 ∂ v = 1 4 ( 1 − u ) {\displaystyle {\frac {\partial N_{3}}{\partial v}}={1 \over 4}(1-u)}