getting error when using diag command

hello i am doing simulation related to duct to control noise and i have structure of matrices, for example i am creating Anr matrices the An and then i want to create Atilta which contains all these matrices according formulas but when i am using diag it gaves me error related to scalar what should i do ?

the formulas are following

*********************

Nmod = 5; % modes in duct 1 to 5
L = 1.2;  % length of duct
K = 0.051; % impedance at one end
zi = 0.315; 
zm = 0.775;
c = 340 ;
roh = 1.225;
S = 1;
eta =1 ;
betan = -(1:Nmod)*pi/L; 
alfa = 1/(2*L)*log((1-K)/(1+K));
Atilta = []; % final matrices

for i = 1:Nmod
%     
  Anr = c * [alfa betan; -betan alfa]; % formula for Anr matrices
%     
  Ani = c*eta*[1 0;0 1];
%     
   An = [Anr -Ani ; Ani Anr]; % Anr and Ani matrices pack in An

    Atilta = diag(Atilta,An);
end

***************

from this i want to create state space matrices

and my Atilta matrix will be like this

but when i am using diag command it will give me error as following

Error using diag

K-th diagonal input must be an integer scalar.
Error in modeNmatrices (line 41)
  Atilta = diag(Atilta,An);

[Aniket]

any one is having idea how to deal with this ?

Answer 1

[Walter Roberson]

When you use the two-argument form of diag(), the second argument needs to be the number of the diagonal. You cannot use diag() to directly modify an existing array.

I am confused: your error message uses diag() but your code uses blkdiag() which can take an array as its second argument.

[Aniket]

no actually i want to use diag but its giving me error so i used blkdiag but its not giving me error but the matrix size is not proper using blkdiag

what should i change in the code to get proper size matrx?

[Azzi Abdelmalek]

From your question, you should use blkdiag. What is the expected size of Atila? From your question it should be 20x40

[Aniket]

yes from my question it is coming 20*40 ,in paper they haven't specified matrix size they just give a matrix structure , its look like in the above diagram

the paper name is

Active Noise Reduction in Ducts of Actuating Dynamics Using Two Periodic Control Signals.

[Aniket]

Atilta size will depend on number of Nmode ...here i am using Nmod = 5