If g 1 , g 2 , g 3 are the contravariant basis vectors in a curvilinear coordinate system, with coordinates of points denoted by ( ξ ξ 1 , ξ ξ 2 , ξ ξ 3 ), then the gradient of the tensor field T is given by (see for a proof.) ∇ ∇ T = ∂ ∂ T ∂ ∂ ξ ξ i ⊗ ⊗ g i