function henonmapx = henon(x,par)
%
% Computes intervals for the Henon map f(x) and the derivative Df(x)  
% for given parameters (parameter intervals) par and for one or a
% sequence of x-values.
% 
% input:  x(1:2,:) 	array of x-values
%	  par(1:2) 	contains the parameters a and b; 
%			must be an interval variable for interval output.
%
% output: henonmapx 		is a structure
%         henonmapx.f(2,:)  	( = f(x) ) 
%         henonmapx.df(2,2,:)  	( = derivative df(x) )
 
  [m,n]=size(x);
  henonmapx.f=[x(2,:)-par(1)*x(1,:).^2+ones(1,n); par(2)*x(1,:)];
  henonmapx.df(:,1,:)=[-2*par(1)*x(1,:); par(2)*ones(1,n)];
  henonmapx.df(:,2,:)=[ones(1,n); zeros(1,n)];
 
% written   05/20/99   D.Stoffer
%

