directional derivative

Noun

 * 1)  A function which measures the rate of change of some other function at any point in a particular direction; formally, the directional derivative of a scalar function $$f(\mathbf{x}) = f(x_1, x_2, \ldots, x_n)$$ along a vector $$\mathbf{v} = (v_1, \ldots, v_n)$$ is the function $$\nabla_{\mathbf{v}}{f}$$ defined by the limit $$\nabla_{\mathbf{v}}{f}(\mathbf{x}) = \lim_{h \to 0}{\frac{f(\mathbf{x} + h\mathbf{v}) - f(\mathbf{x})}{h}}$$.

Translations

 * Italian: derivata direzionale
 * Polish: