21. This is a gradient \ nabla ^ a t is everywhere timelike and future-directed. 22. Where \ nabla _ \ mu is the general-relativistic covariant derivative of a spinor. 23. Further \ rho is the fluid density and \ nabla \ times is the curl operator. 24. Implying that the vector \ nabla \ psi is normal to the curve \ psi = C. 25. Where the \ nabla on the right denotes the gradient and \ cdot is the dot product. 26. If all the elements of \ nabla f are desired, then n function evaluations are required. 27. An arbitration request regarding User : Nabla has now closed and the decision can be read here. 28. This tells us that \ nabla coincides with D when acting on objects with only internal indices. 29. In other words, the unary " modal " operations \ nabla _ j are lattice endomorphisms. 30. The symbol \ partial _ k denotes partial derivative, while \ nabla _ k denotes covariant derivative.
