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One approach to cross ratio interprets it as a homography that takes three designated points to 0, 1, and ∞. Under restrictions having to do with inverses, it is possible to generate such a mapping with ring operations in the projective line over a ring. The cross ratio of four points is the evaluation of this homography at the fourth point.
In statistics, a contingency table (also known as a cross tabulation or crosstab) is a type of table in a matrix format that displays the multivariate frequency distribution of the variables. They are heavily used in survey research, business intelligence, engineering, and scientific research.
The cross-ratio (,;,) = () is a ratio of division ratios, or a double ratio. Setting the double ratio to minus one means that when t(c) + t(d) = 0, then c and d are harmonic conjugates with respect to a and b. So the division ratio criterion is that they be additive inverses.
One application of cross ratio defines the projective harmonic conjugate of a triple a, b, c, as the element x satisfying (x, a, b, c) = −1. Such a quadruple is a harmonic tetrad . Harmonic tetrads on the projective line over a finite field GF( q ) were used in 1954 to delimit the projective linear groups PGL(2, q ) for q = 5, 7, and 9, and ...
A data set would contain one such triple for each rock in a sample of rocks. In high throughput sequencing, data obtained are typically transformed to relative abundances, rendering them compositional. In probability and statistics, a partition of the sampling space into disjoint events is described by the probabilities assigned to such events.
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Two functions and () are proportional if their ratio () is a constant function. If several pairs of variables share the same direct proportionality constant, the equation expressing the equality of these ratios is called a proportion , e.g., a / b = x / y = ⋯ = k (for details see Ratio ).
The metric distance between two points inside the absolute is the logarithm of the cross ratio formed by these two points and the two intersections of their line with the absolute. In mathematics, a Cayley–Klein metric is a metric on the complement of a fixed quadric in a projective space which is defined using a cross-ratio.
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