Nabla 算子，係向量微積分裏面嘅一個算子，符號係 ∇ {\displaystyle \nabla } 。佢嘅定義係：
∇ = ∑ i = 1 n e → i ∂ ∂ x i = ( ∂ ∂ x 1 , … , ∂ ∂ x n ) {\displaystyle \nabla =\sum _{i=1}^{n}{\vec {e}}_{i}{\partial \over \partial x_{i}}=\left({\partial \over \partial x_{1}},\ldots ,{\partial \over \partial x_{n}}\right)}
譬如喺 R 3 {\displaystyle \mathbb {R} ^{3}} 平面裏面：
∇ = i ∂ ∂ x + j ∂ ∂ y + k ∂ ∂ z = ( ∂ ∂ x , ∂ ∂ y , ∂ ∂ z ) {\displaystyle \nabla =\mathbf {i} {\frac {\partial }{\partial x}}+\mathbf {j} {\frac {\partial }{\partial y}}+\mathbf {k} {\frac {\partial }{\partial z}}=\left({\frac {\partial }{\partial x}},{\frac {\partial }{\partial y}},{\frac {\partial }{\partial z}}\right)}
。佢嘅定義係：
平面裏面：
