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 Conversely, it is trivially true that every operator of the form "B* B" is non-negative. Therefore, an operator "T" is non-negative if and only if "T" = "B* B" for some "B" (equivalently, "T" = "CC*" for some "C"). The Cholesky factorization provides another particular example of square root, which should not be confused with the unique non-negative square root. If "T" is a non-negative operator on a finite-dimensional Hilbert space, then all square roots of "T" are related by unitary transformations. More precisely, if "T" = "A*A" = "B*B", then there exists a unitary "U" such that "A" =