clear all
q=[0.78 -0.02 -.12 -.14
0 .86 -.04 0.06
0 0 .72 -.08
0 0 0 .74];
d=diag(q);
q=q+q'-diag(d);
%%% to change the condition number
%q=q^10;
%q=2*q/norm(q,inf);
%%% end to change the condition number
b=[.76 .08 1.12 .68]';
xc=zeros(4,1);
gc=q*xc-b;
f=.5*xc'*q*xc-b'*xc;
plot(norm(xc),f,'bx')
hold on
iter=0;
while norm(gc) > 1e-8,
   iter=iter+1;
   alpha=(gc'*gc)/(gc'*q*gc);
   xc=xc-alpha*gc;
   gc=q*xc-b;
   flast=.5*xc'*q*xc-b'*xc;
   f=[f flast];
   plot(norm(xc),flast,'bx')
end
hold off