A point where a function has zero gradient. A function f(x1, x2,…, xn) of one or more variables is said to have a stationary value at the point (a1, a2,…, an) if all the partial derivatives of f with respect to x1, x2,…, xn vanish when (x1, x2,…, xn)=(a1, a2,…, an). The point (a1, a2,…, an) is a stationary point. The stationary point is a maximum (or minimum) if, for all neighbouring points, f(x1, x2,…, xn) is less (or greater) than f(a1, a2,…, an). The stationary point is a minimax if there are points in the neighbourhood at which f(x1, x2,…, xn) < f(a1, a2,…, an), and points in the neighbourhood at which f(x1, x2,…, xn) > f(a1, a2,…, an). For example, x2+3y2 has a minimum (stationary) point at (0, 0),−2x2−5y2 has a maximum point at (0, 0), and 2x2−5y2 has a minimax point at (0, 0).