geth2.m

来自「控制系统计算机辅助设计——MATLAB语言与应用(源代码）」· M 代码 · 共 29 行

function [v,ierr]=geth2(G)
%GETH2 computes the H2 norm of a system using Astrom recursive method.
%  
%[v,ierr]=GETH2(G) 
%     where G is the system model, 
%       v is the H2 norm.  
%       If ierr=1, then the system is unstable, and v is useless.
%
%  See Also: NORMH2, COVAR

%Designed by Professor Dingyu Xue
%Northeastern University, Shenyang 110004, P R China
%first drafted in 1990, revised for LFC book, 2002
G=tf(G); num=G.num{1}; den=G.den{1};
ierr=0; v=0; n=length(den); 
if abs(num(1))>eps
   disp('System not strictly proper'); 
   ierr=1; return
else, a1=den; b1=num(2:length(num)); end
for k=1:n-1
  if (a1(k+1)<=eps), ierr=1; return
  else,
     aa=a1(k)/a1(k+1); bb=b1(k)/a1(k+1);
     v=v+bb*bb/aa; k1=k+2;
     for i=k1:2:n-1
        a1(i)=a1(i)-aa*a1(i+1);
        b1(i)=b1(i)-bb*a1(i+1);
end, end, end
v=sqrt(0.5*v);