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In probability and statistics, given two stochastic processes and , the cross-covariance is a function that gives the covariance of the one process with the other at pairs of time points. With the usual notation ''E'' for the expectation operator, if the processes have the mean functions and , then the cross-covariance is given by : Cross-covariance is related to the more commonly used cross-correlation of the processes in question. In the case of two random vectors and , the ''cross-covariance'' would be a square ''n'' by ''n'' matrix with entries Thus the term ''cross-covariance'' is used in order to distinguish this concept from the "covariance" of a random vector ''X'', which is understood to be the matrix of covariances between the scalar components of ''X'' itself. In signal processing, the cross-covariance is often called cross-correlation and is a measure of similarity of two signals, commonly used to find features in an unknown signal by comparing it to a known one. It is a function of the relative time between the signals, is sometimes called the ''sliding dot product'', and has applications in pattern recognition and cryptanalysis. (詳細はrandom vectors ''X'' and ''Y'', each containing random elements whose expected value and variance exist, the cross-covariance matrix of ''X'' and ''Y'' is defined by : where ''μX'' and ''μY'' are vectors containing the expected values of ''X'' and ''Y''. The vectors ''X'' and ''Y'' need not have the same dimension, and either might be a scalar value. Any element of the cross-covariance matrix is itself a "cross-covariance". 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Cross-covariance」の詳細全文を読む スポンサード リンク
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