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For pairs of objects that are not both points, the distance can most simply be defined as the smallest distance between any two points from the two objects, although more complicated generalizations from points to sets such as Hausdorff distance are also commonly used. [6] Formulas for computing distances between different types of objects include:
The graph (bottom, in red) of the signed distance between the points on the xy plane (in blue) and a fixed disk (also represented on top, in gray) A more complicated set (top) and the graph of its signed distance function (bottom, in red).
For two objects and having descriptors, the similarity is defined as: = = =, where the w i j k {\displaystyle w_{ijk}} are non-negative weights usually set to 1 {\displaystyle 1} [ 2 ] and s i j k {\displaystyle s_{ijk}} is the similarity between the two objects regarding their k {\displaystyle k} -th variable.
A metric on a set X is a function (called the distance function or simply distance) d : X × X → R + (where R + is the set of non-negative real numbers). For all x, y, z in X, this function is required to satisfy the following conditions: d(x, y) ≥ 0 (non-negativity) d(x, y) = 0 if and only if x = y (identity of indiscernibles.
A metric or distance function is a function d which takes pairs of points or objects to real numbers and satisfies the following rules: The distance between an object and itself is always zero. The distance between distinct objects is always positive. Distance is symmetric: the distance from x to y is always the same as the distance from y to x.
The distance (or perpendicular distance) from a point to a line is the shortest distance from a fixed point to any point on a fixed infinite line in Euclidean geometry. It is the length of the line segment which joins the point to the line and is perpendicular to the line. The formula for calculating it can be derived and expressed in several ways.
The definition of the Hausdorff distance can be derived by a series of natural extensions of the distance function (,) in the underlying metric space M, as follows: [7] Define a distance function between any point x of M and any non-empty set Y of M by: (,) = {(,)}.
The distance is measured by a function called a metric or distance function. [1] Metric spaces are the most general setting for studying many of the concepts of mathematical analysis and geometry . The most familiar example of a metric space is 3-dimensional Euclidean space with its usual notion of distance.