D𝐯f(𝐱)=∇f(𝐱)⊺𝐯D_\mathbf{v} f(\mathbf{x}) = \nabla f(\mathbf{x})^{\intercal}\mathbf{v}

where ∇f(𝐱)\nabla f(\mathbf{x}) denotes the gradient

References:

  1. https://www.chrismusco.com/amlds2023/notes/lecture06.html