How to define a matrix which changes its size in every iteration of loop?

T = 50;    %total iteration 
x = randn(T,1); %input
pw =[0,0,0,0,0,1,-0.3,0.2];    % primary path TF 
d = filter(pw, 1, x);          % desiresd input
mu = 0.1;  %step size
g = 1e-12; %gamma
%p = 2;     %projection order
N = 8;    %no of taps
Pmax = 4;
w = zeros(N,1); % weights of controller
y = zeros(1,T); % output of controller
%Xi = zeros(p,N); %input matrix  
e_cont = zeros(T,1); %residual noise
p = zeros(T,1);
p(1)=Pmax;
for i=1:T
    Xi(2:p(i),:) = Xi(1:p(i),:);
    Xi(1,:) = [ x(i:-1:max(i-N+1,1)).',zeros(1,max(N-i,0)) ];
    di = transpose([ d(i:-1:max(i-p(i)+1,1)).',zeros(1,max(p(i)-i,0)) ]);
    Yi = Xi*w;
    err= di-Yi;
    sqe = err.^2;
    UT = (mu*p(i)+2)*var/(2-mu);
    LT = (mu*(p(i)-1)+2)*var/(2-mu);
    if sqe(p(i)) > UT
        p(i+1) = min(p(i)+1,Pmax);
    elseif sqe(p(i))<= LT
        p(i+1) = max(p(i)-1,1);
    else
        p(i+1) = p(i);
    end
    w = w + mu*Xi'*inv(g*eye(p(i))+Xi*Xi')*(di-Yi);
    e_cont(i)= err(p(i));
end;

[darova]

WHy do you need to change matrix size? Can't you create larger one?

Changing size of a matrix is a bad idea

[zahid fazal]

no, this is evolving order affine projection algorithm which changes size of input matrix(Xi) every time whenever projection order (p) changes.

[Stephen23]

Original question by zahid fazal retrieved from Google Cache:

https://web.archive.org/web/20210223064945/https://webcache.googleusercontent.com/search?q=cache%3AvhRjTWsjouUJ%3Ahttps%3A%2F%2Fwww.mathworks.com%2Fmatlabcentral%2Fanswers%2F751039-how-to-define-a-matrix-which-changes-its-size-in-every-iteration-of-loop

https://web.archive.org/web/20210223070420/https://www.mathworks.com/matlabcentral/answers/751039-how-to-define-a-matrix-which-changes-its-size-in-every-iteration-of-loop

How to define a matrix which changes its size in every iteration of loop?

T = 50;    %total iteration 
x = randn(T,1); %input
pw =[0,0,0,0,0,1,-0.3,0.2];    % primary path TF 
d = filter(pw, 1, x);          % desiresd input
mu = 0.1;  %step size
g = 1e-12; %gamma
%p = 2;     %projection order
N = 8;    %no of taps
Pmax = 4;
w = zeros(N,1); % weights of controller
y = zeros(1,T); % output of controller
%Xi = zeros(p,N); %input matrix  
e_cont = zeros(T,1); %residual noise
p = zeros(T,1);
p(1)=Pmax;
for i=1:T
    Xi(2:p(i),:) = Xi(1:p(i),:);
    Xi(1,:) = [ x(i:-1:max(i-N+1,1)).',zeros(1,max(N-i,0)) ];
    di = transpose([ d(i:-1:max(i-p(i)+1,1)).',zeros(1,max(p(i)-i,0)) ]);
    Yi = Xi*w;
    err= di-Yi;
    sqe = err.^2;
    UT = (mu*p(i)+2)*var/(2-mu);
    LT = (mu*(p(i)-1)+2)*var/(2-mu);
    if sqe(p(i)) > UT
        p(i+1) = min(p(i)+1,Pmax);
    elseif sqe(p(i))<= LT
        p(i+1) = max(p(i)-1,1);
    else
        p(i+1) = p(i);
    end
    w = w + mu*Xi'*inv(g*eye(p(i))+Xi*Xi')*(di-Yi);
    e_cont(i)= err(p(i));
end;

[Rena Berman]

(Answers Dev) Restored edit

Answer 1

[Walter Roberson]

It is legal to change the size of a matrix inside a loop, including being legal to let it grow one element at a time every iteration. However, it is more efficient if you can create the matrix at full size ahead of time. Sometimes much more efficient.

The problem with your code is that you do not initialize the variable Xi but you have

    Xi(2:p(i),:) = Xi(1:p(i),:);

That requires that rows 1 to Pmax and all columns of Xi are initialized before the statement is executed -- but Xi is undefined here.

Also, the right hand side has p(i)-1+1 = p(i) rows, but the left hand side has p(i)-2+1 = p(i)-1 rows . This is a mismatch: you would be trying to store 4 rows of data into a location that only holds three rows.

[zahid fazal]

yes sir fist line of code inside loop is mistakenly written wrong here.

actually it is

Xi(2:p(i),:) = Xi(1:p(i)-1,:);

[zahid fazal]

sir i tried to code for evolving order affine projection algorithm, which changes size of imput matrix (Xi) at every iteration acoording to p. what could be possible solution for it?

note: Xi is p rows N column matrix.

[Walter Roberson]

I have not heard of "evolving order affine projection".