The vector gradient operator. In rectangular coordinates,
where i, j, k are unit vectors in the x, y, z directions. is the gradient of the scalar field U.
The operator , the Laplacian, appears frequently:
As an operator on a vector field V, is called the divergence, and is called the curl. Del is also called nabla and the vector operator. See also Figure C-14 for expressions using del in cylindrical and spherical coordinates.