Calculates the "sign" function
sig = +1 if x[k] > +b else 0, sig = -1 if x[k] < -b else 0,component-wise.
function sign_gtlt extends Icons.Function; input Real[:] x "argument"; input Real b(min = 0) "threshold value"; output Real[size(x, 1)] y "characteristic function of abs(x) > b"; end sign_gtlt;