function minvalue=ps5p2_zupperbar_zero(tildez);

global ALPHAX ALPHAZ ALPHATILDEZ B  C X1STAR SELECT OPTIONS;

% we know that the function goes to minus infinity as theta2 goes to 0,
% so we can find theta2lower at which the function is negative
% we also know that the function goes to plus infinity as theta2 goes to1,
% so we can find theta2upper at which the function is positive
theta2lower=find_bound_converge('ps5p2_stage2_zero','right',-1,0.1,1,0,tildez);
theta2upper=find_bound_converge('ps5p2_stage2_zero','left',1,0.1,1,1,tildez);
[theta2min,minvalue]=fminbndn('ps5p2_stage2_zero',0.5,theta2upper,1,OPTIONS,[],tildez);

      