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A notion used across various fields of scientific study that shows the relation between members of two or more groups of data.

Visual comparison of convolution, cross-correlation and autocorrelation. For the operations involving function f, and assuming the height of f is 1.0, the value of the result at 5 different points is indicated by the shaded area below each point. Also, the vertical symmetry of f is the reason ${\displaystyle f*g}$ and ${\displaystyle f\star g}$ are identical in this example.