how to stop overwriting a matrix in a for loop in matlab

Hello all,

i'm stuck with this code.

I am trying to get the value of M.

M is the product of three matrices, iterated and multiplied 100 times. please see below.

    for n  =1:100
        y = OUT.lin.matin(:,:,n);               %gets valiue from a stored array
        %y is a unitary matrix
           x = OUT.lin.db0(n);                      %gets valiue from a stored array
          % x is a scalar
        w =[exp(1i*x),exp(1i*-x)];        % creating the exponential 
     
        k = diag(w);                                     % creating a diagonal matrix of W

        M = y*k*y'; 
end

I think M overrides each iteration, but i would like to get the results from the 100 iterations. Kindly assist.

Thanks in advance.

Answer 1

[KSSV]

M = zeros([],[],100) ; % give exact row and column size 
    for n  =1:100
        y = OUT.lin.matin(:,:,n);               %gets valiue from a stored array
        %y is a unitary matrix
           x = OUT.lin.db0(n);                      %gets valiue from a stored array
          % x is a scalar
        w =[exp(1i*x),exp(1i*-x)];        % creating the exponential 
     
        k = diag(w);                                     % creating a diagonal matrix of W

        M(:,:,n) = y*k*y'; 
end

[Reinhardt RADING]

Thanks for your input.

When i implement it, I'm getting this error.

Unable to perform assignment because the size of the left side is 0-by-0 and the size of the right side is 2-by-2.

Error in DGD (line 109)

M(:,:,n) = y*k*y';

[Reinhardt RADING]

Could you also kindly elaborate on

"% give exact row and column size "

Thanks.

[KSSV]

If the RHS is of size 2X2 use:

M = zeros(2,2,100) ; % give exact row and column size 

[Reinhardt RADING]

Thanks this worked.

One more question! (Sorry,i'm still a novice in Matlab)

does the value of result of M(:,:,100) gives the multiplication for all values.

i.e

M1*M2*M3...M100

since

M1=y1*w1*y1'

M2 =y2*w2*y2'

.

.

M100=y100*w100*y100

Or do have to create another loop to get the product of every term?

Thanks again.