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I'm trying to create a 40000x40000 sparse matrix with 2 diagonals. This is my code:

n = 200;
s = n*n;

for j=1:2
    for i=1:(s-1)
        if mod(i,n) == 0
           u(i,j) = 0;
            u(i,j) = 1;
c = [-1;1];

Y = spdiags(u,c,s,s);

When I try to run it i get the following message:

??? Index exceeds matrix dimensions.

Error in ==> spdiags at 114
         a((len(k)+1):len(k+1),:) = [i i+d(k) B(i+(m>=n)*d(k),k)];

Error in ==> uppg3 at 26
Y = spdiags(u,c,s,s);

I don't see where the problem is. Would really appreciate some help.

Best regards

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