Less-than sign Less-than sign The "less-than sign" is a mathematical symbol that denotes an inequality between two values. The widely adopted form of two equal-length strokes connecting in an acute angle at the left, <, has been found in documents dated as far back as the 1560s. In typical mathematical usage, the less-than sign is typically placed between the two values being compared and signals that the first number is less than the second number. Examples of typical usage include "½ < 1" and "−2 < 1". Since the development of computer programming languages, the less-than sign and the greater-than sign have
Degrees of freedom (statistics) the vectors of residuals are constrained to lie in a space of smaller dimension than the number of components in the vector. That smaller dimension is the number of degrees of freedom for error, also called residual degrees of freedom. Perhaps the simplest example is this. Suppose are random variables each with expected value μ, and let be the "sample mean." Then the quantities are residuals that may be considered estimates of the errors "X" − μ. The sum of the residuals (unlike the sum of the errors) is necessarily 0. If one knows the values of any "n" −