nbastrom.m

以《随机控制理论导论》为基础

function I=NB(num,den);

% Calculation of Noise Bandwidth using Astrom's theory;
% num - numerator coeff. array of TF;
% den - denominator coeff. array of TF;
% Same length of num and den is required;
% Written by Paul Wong, Mar 7th, 2008

% Important!!!
% When dealing with symbolic parameters, Both num & den have to be transformed into sym format first.


I=0;
A=den;
B=num;
n=length(num);
for k=2:length(num)
    if isnumeric(A(k-1,1)) && A(k-1,1)<=0
        error('Not a steady system. Eigen coefficient(s) not positive.')
    end
    for i=1:n-k+1
        A(k,i)=A(k-1,i)-(A(k-1,n-k+2)/A(k-1,1))*A(k-1,n+3-k-i);
        B(k,i)=B(k-1,i)-(B(k-1,n-k+2)/A(k-1,1))*A(k-1,n+3-k-i);
    end
end
for i=1:n
    I=I+B(i,n-i+1)^2/A(i,1);
end
I=I/A(1,1);