Why do I receive error for reshape function?

I am using the following code below, however, I keep getting geting the error message for reshape function. How would the code or reshape function be changed to stop the error?

>> s = 1/sqrt(2);
A = [1 1 1 0 0 0 0 0 0; 0 0 0 0 0 0 1 1 1; 1 0 0 1 0 0 1 0 0; 0 0 1 0 0 1 0 0 1; s s 0 s 0 0 0 0 0; 0 0 0 0 0 s 0 s s; 0 0 0 s 0 0 s s 0; 0 s s 0 0 s 0 0 0];
b = [6; 24; 12; 18; 4.9497; 16.2634; 13.4350; 7.7781];

k = 1:20;
X = kaczmarz(A,b,k);
figure(1)
for i=1:kmax, subplot(4,5,i), imagesc(reshape(X(:,i),N,N)), end
Error using reshape
Number of elements must not change. Use [] as one of the size inputs
to automatically calculate the appropriate size for that dimension.

[Chunru]

Check the size of X before figure(1):

size(X) 

Check if the first dimension of X is equal to N*N

[Scott MacKenzie]

I suspect the issue is that X(:,i) does not have exactly NxN elements.

[Ryan]

I've checked the size of X:

size(X)

ans =

     9     7

>> N*N

ans =

        4096

What would I need to change X size to be to get figure(1)?

Answer 1

[KSSV]

The number of elements in X(:,j) is not equal to N*N, thats why you are getting error.

N = 3 ; 
X = rand(10) ; 
x = reshape(X(:,1),N,N) ; % this will lead to error 

Error using reshape
Number of elements must not change. Use [] as one of the size inputs to automatically calculate the appropriate size for that dimension.

See to it that the number of elements should not change. You may use imresize to achieve this.

[m,n] = size(X) ;
X = imresize(X,[N*N,n]) ; 
imagesc(reshape(X(:,1),N,N)) ;  % this will work

[Ryan]

In my next line of code I've used

k = [50,100,200,400,800];
X = kaczmarz(A,b,k);
e = zeros(length(k),1)
 for i=1:length(k), e(i) = norm(x-X(:,i),inf); end
e
figure(2), semilogy(k,e)

This has created a matrix dimentions must agree error?

[KSSV]

It would be because the dimensions (number of rows) in x and X are different. You can change the dimensions of x or use same X as previous.

[Ryan]

Great! All working now, thanks for the help!