This is a formula in college advanced mathematics. Where gradf stands for gradient, which is a vector, that is, the function changes fastest along the direction of this gradient at (x, y, z), and the rate of change is the maximum modulus of this gradient. DIV, that is, finding the divergence of the previous vector, can be used to describe the divergence of the vector field at various points in space.

In vector calculus, the gradient of scalar field is a vector field. The gradient of a point in the scalar field points to the fastest growing direction of the scalar field, and the length of the gradient is the maximum change rate. More strictly speaking, the gradient of a function from Euclidean space Rn to R is the best linear approximation of a point in Rn. In this sense, gradient is a special case of Jacobian matrix.