A displacement vector describes a change in parameter values. For a one-dimensional parameter w, δw produces a loss change δL; for sufficiently small changes, δL ≈ (dL/dw)δw. Reducing loss therefore requires moving opposite the derivative. section 3.3.1
A two-parameter step
For L(w₀,w₁)=2w₀²+3w₁² at P=(3,4), the loss is 66. The displacement vector [-12,-24]ᵀ points along the negative gradient and gives the greatest local reduction.
