The normal vector, often simply called the "normal", to a surface is a vector perpendicular to it. Often, the normal unit vector is desired, which is sometimes known as the "unit normal".

The normal vector at point (x0, y0) on a surface z = f(x ,y) is given by

where and are partial derivatives.

A normal vector to a plane is specified by

is given by

where denotes the gradient.

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