function out = paraf(x, y, mode)% Parabolic surface for illustrating steepest descent, Newton,% and LM directions.% J.-S. Roger Jang, June 9, 1996if nargin <= 2, mode = 0; enda=1;b=1;c=1;d=-1;e=1;if mode == 0,		% return function value	out=a*x.^2+b*x.*y+c*y.^2+d*x+e*y;elseif mode == 1,	% return gradient	out = [2*a*x+b*y+d; b*x+2*c*y+e];elseif mode == 2,	% return Hessian	out = [2*a b; b 2*c];else	error('Wrong mode value!');end