function lim=extrapolate(e)
% lim=extrapolate(e)
% compute lim assuming that e(i+1)-lim = c*(e(i)-lim)
% if e is matrix extrapolate rows

% (x-lim)/(y-lim)=(y-lim)/(z-lim)    x=e(i) y=e(i+1) z=e(i+2)
% (x-lim)*(z-lim)=(y-lim)^2
%  x*z - lim*(x+z) + lim^2 = y^2 - lim*2y + lim^2
% lim = (x*z - y*y)/(x+z-2*y)

i=1:size(e,2)-2;
x=e(:,i); y=e(:,i+1); z=e(:,i+2);
lim=(x.*z - y.*y)./((x-y)+(z-y));