function ps72(a,flg)
if nargin<1, a=1; end
flg=(nargin>1);
z=tf('z');
p=ss(a,[1 1],[1;1],[0 1;1 0],-1);
if abs(a-1)<1,
    P=0;
else
    P=a^2-2*a;
end
F=-(1+P*a)/(1+P);
if flg,               % strictly causal controller design
    D=0;
    [K1,~,GAM1]=h2syn(p,1,1);
else
    D=P*((P+1)*F-1)/(P+1)^2;
    [K1,~,GAM1]=h2syn6245(p,1,1);
end
K=D-(F-D)^2/(z-a-2*F+D);
GAM2=norm(lft(p,K));
GAM=sqrt(D^2+P*(1+D)^2+(1+P)*P*(F-D)^2);

fprintf('GAMMA: analytical %f, numerical %f, actual %f\n',GAM,GAM1,GAM2)
fprintf('optimality test: %e~0\n',h2synchk(p,K))
K=tf(K)
K1=tf(K1)