function y1 = kepler0(epsil)
%
%   Usage:
%   y0 = kepler0( epsil )   starting point for the kepler problem
%                           with eccentricity epsil ( in (0,1) ).
%                           Default value = 0.6. Period = 2*pi.
%   y0 = [q1 q2 p1 p2](0).
%
%   See pages 131-134  of
%   L.Brugnano, F.Iavernaro.
%   Line Integral Methods for Conservative Problems.
%   Chapman and Hall/CRC - 2015
%   Series: Monographs and Research Notes in Mathematics.
%
if nargin==0
    epsil = 0.6;
elseif epsil<0 || epsil >=1 
    error('epsil in [0,1)'), 
end
y1 = [1-epsil 0 0 sqrt((1+epsil)/(1-epsil))];
return
