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function [nh]=h2norm(g,tol)
//
// /+00
// 2 | *
// |g| =1/(2*%pi).|trace[g(jw).g(jw)]dw
// 2 |
// /-00
// Copyright INRIA
if type(g)==1,if norm(g)==0,nh=0,return,end,end,
[lhs,rhs]=argn(0),
if rhs==1 then tol=1000*%eps,end;
g1=g(1);
if g1(1)=='lss' then
if norm(g(5))>0 then error('non zero D'),end;
sp=spec(g(2)),
if maxi(real(sp))>=-tol then
error('unstable system!'),
end,
w=obs_gram(g(2),g(4),'cont'),
nh=abs(sqrt(sum(diag(g(3)'*w*g(3))))),return,
else,
num=g(2),den=g(3),
s=poly(0,varn(den)),
[t1,t2]=size(num),
for i=1:t1,
for j=1:t2,
n=num(i,j),d=den(i,j),
if coeff(n)==0 then
nh(i,j)=0,
else
if degree(n)>=degree(d) then
error('improper system'),
end
pol=roots(d),
if maxi(real(pol))>-tol then
error('unstable system!'),end,
nt=horner(n,-s),dt=horner(d,-s),
nh(i,j)=residu(n*nt,d,dt),
end,
end
end
nh=sqrt(sum(nh)),return,
end
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