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Signum function = . In mathematics, the sign function or signum function (from signum, Latin for "sign") is a function that has the value −1, +1 or 0 according to whether the sign of a given real number is positive or negative, or the given number is itself zero.
This function is also sometimes called the sign function, although this may lead to confusion with the sine function. In mathematical expressions, the signum function is often represented as sgn." Also, I think the article title should be "Signum function", not "Sign function". Isheden 16:59, 7 March 2012 (UTC)
The matrix sign function is a generalization of the complex signum function = {() >, <, to the matrix valued analogue ().Although the sign function is not analytic, the matrix function is well defined for all matrices that have no eigenvalue on the imaginary axis, see for example the Jordan-form-based definition (where the derivatives are all zero).
The sign, signature, or signum of a permutation σ is denoted sgn(σ) and defined as +1 if σ is even and −1 if σ is odd. The signature defines the alternating character of the symmetric group S n .
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