Error: Index exceeds the number of array elements. Index must not exceed 1.

Hello, I am trying to build a code that identifies a system using recursive least squares and i created an function based on the theory

function[thetak,Pk]=real_time_identification_try2(u,y,Pk_1,thetak_1,alphak)
%function determines theta and the covariance
%u= data input
%y=data output
%n number of zeros
%m number of poles
%alpha = forgetting factor
%vector a_k(vector with inputs and outputs)
a_k=[u, -y];
%implementation
thetak= thetak_1+((Pk_1* a_k.')/((1/alphak)+a_k*Pk_1*a_k.'))*(y(k-a_k*thetak_1));
Pk = Pk_1 -((Pk_1*a_k.'*a_k*Pk_1)/((1/alphak)*a_k*Pk_1*a_k.'));
end

And am calling the function in this script

clc 
clear
load linearidade2.mat
u=simout.Data(:,1);
y=simout.Data(:,2);
N = length(u);
%poles and zeros
n= 2;
m= 0;
alphak=0.99;
%setup covariance and theta
P0=100*eye(n+m+1);
theta0 = 0;
%incial conditions
Pk = P0;
thetak = theta0;
for k= max(n,m)+1: N
    %input data
    u=(k:-1:k-m);
    y=(k-1:-1:k-n);
    % past inputs
    for j = 0:m+1
        if k-j > 0
            a_k(j+1) = u(k-j); % Insert u(k), u(k-1), ..., u(k-m) em a_k
        end
    end
    % past outputs
    for  j=1:n
        if k-j > 0
            a_k(m+j+1) = -y(k-j); %insert y(k),y(k-1),...,y(k-n) em a_k
        end
    end
    [thetak,Pk] = real_time_identification_try2(u, y,Pk,thetak, alphak);
    
end

Index exceeds the number of array elements. Index must not exceed 1.

% % updating the covariance matix for k+1
for j=0:m+n
    if k-j > 0;
        P = Pk;
        theta = thetak;
    end
end
[thetak,Pk]=real_time_identification_try2(u,y,Pk_1,thetak_1,alphak)
% Create the transfer function with estimated parameters
G_estimated = tf([theta(1:1:m+1)], [1 theta(m+2:1:n+m+1)], 0.010);
disp('Estimated Transfer Function:');
G_estimated
% Display final estimated parameters
disp('Final estimated parameters:');
disp(theta);

Thank you in advance

[Hitesh]

Hi @Aliya Magno

Could you share your .mat file, so that I can reproduce this error ?

[Aliya Magno]

hi@Hitesh, of course

[DGM]

You initialize u and y from the matfile

u=simout.Data(:,1);
y=simout.Data(:,2);

but then you overwrite the data with some indices

%input data
u=(k:-1:k-m);
y=(k-1:-1:k-n);

There's also a code analyzer warning on this line:

Pk = Pk_1 -((Pk_1*a_k.'*a_k*Pk_1)/((1/alphak)*a_k*Pk_1*a_k.'));

Parenthesize the multiplication of a_k with its transpose to ensure the result is Hermetian

I don't think that's what's causing your indexing error, but you should double check that it's not causing any issues for your intended purpose.

[Aliya Magno]

thank you this parte was indeed incorrect!

Answer 1

[Cris LaPierre]

When the first for loop starts, your variables have the following values

• k = 3
• j = 0
• m = 0
• n = 2

So the value of u is u=(k:-1:k-m) which is 3. Then inside the look that defines a_k, you index u using u(k-j), which is u(3). But u is a scalar (one element). Here is code that recreates the error.

u=3;
u(3)

Index exceeds the number of array elements. Index must not exceed 1.