Re: [Gretl-users] idempotence and symmetry

On Mon, 11 May 2009, Sebastiano Putoto wrote: Example of checking exact equality: <script> set seed 567432 matrix m1 = mnormal(10,10) matrix m2 = mnormal(10,10) # Does m2 equal m1? scalar meq = (m1 = m2) set seed 567432 matrix m3 = mnormal(10,10) # Does m3 equal m1? scalar meq = (m1 = m3) </script> However, depending on the context, "near enough" might do: <script> matrix x = mnormal(10,2) matrix xx = x'x matrix xxi = inv(xx) matrix xxii = inv(xxi) # Does xxii equal xx (No)? meq = (xx = xxii) # Does xxii approximately equal xx? tol = 1.0e-14 scalar approx_eq = abs(xx - xxii) < tol </script> (Obviously, "approximately equal" could be defined in various ways.) Allin Cottrell