Square Root Day September 9, 1981 (9/9/81). Gordon remains the holiday's publicist, sending news releases to world media outlets. Gordon's daughter set up a Facebook group where people can share how they were celebrating the day. One suggested way of celebrating the holiday is by eating square radishes, or other root vegetables cut into shapes with square cross sections (thus creating a "square root"). Square Root Day occurs on the following dates each century: The number of years between consecutive Square Root Days in a century are consecutive odd numbers: 3, 5, 7, 9, 11, 13, 15, 17. This illustrates the fact that
Square root of a matrix is an "n" × "n" complex matrix "ρ" that is positive semidefinite with trace 1. If "ρ" can be expressed as where formula_36 and ∑ "p" = 1, the set is said to be an ensemble that describes the mixed state "ρ". Notice {"v"} is not required to be orthogonal. Different ensembles describing the state "ρ" are related by unitary operators, via the square roots of "ρ". For instance, suppose The trace 1 condition means Let and "v" be the normalized "a". We see that gives the mixed state "ρ". In the Unscented Kalman Filter (UKF), the square root of