双1次曲面
u {\displaystyle u} 方向および v {\displaystyle v} 方向の偏微分は,以下の通り。
∂ S ∂ u = ( v − 1 ) P 0 + ( 1 − v ) P 1 + ( − v ) P 2 + ( v ) P 3 {\displaystyle {\frac {\partial S}{\partial u}}=(v-1)P_{0}+(1-v)P_{1}+(-v)P_{2}+(v)P_{3}}
∂ S ∂ v = ( u − 1 ) P 0 + ( − u ) P 1 + ( 1 − u ) P 2 + ( u ) P 3 {\displaystyle {\frac {\partial S}{\partial v}}=(u-1)P_{0}+(-u)P_{1}+(1-u)P_{2}+(u)P_{3}}