% [xs,xsf] = phxs(x,ar,af,xsi)
function [xs,xsf] = phxs(x,ar,af,xsi)

N = lge(x);
x = abs(x);
xs(1) = xsi;

for n = 2:N,
  if(x(n) > xs(n-1))
    xs(n) = ar*x(n) + (1-ar)*xs(n-1);
  else
    xs(n) = af*x(n) + (1-af)*xs(n-1);
  end;
end;
xsf = xs(N);