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

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zahid fazal 2021 年 2 月 20 日
コメント済み: Rena Berman 2021 年 5 月 6 日 20:40
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;
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Rena Berman 2021 年 5 月 6 日 20:40
(Answers Dev) Restored edit

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### 採用された回答

Walter Roberson 2021 年 2 月 20 日
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.
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Walter Roberson 2021 年 2 月 20 日
I have not heard of "evolving order affine projection".

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