CODEWITHSUNDEEP
matlab
colddie
colddie

Reputation: 1049

MATLAB error: Matrix is too large to return linear indices

I am trying to find all non-zeros elements in a large sparse matrix K(19683000x19683000). I used find to first return the linear indices.

val = K(K~=0);
inds = find(K~=0);
[j, i] = ind2sub(size(K), inds);
% [j, i] = find(K~=0);
i = full(i);
j = full(j);

This gave some error:

Error using find
Matrix is too large to return linear indices.
Use [i,j] = find(S) for sparse matrix.
Error in (line 82)
inds = find(K~=0);
Error in run (line 64)
evalin('caller', [script ';']);

Any idea what is happening and how I can avoid it?

Upvotes: 3

Views: 185

Answers (1)

Luis Mendo
Luis Mendo

Reputation: 112699

I am not familiar with that error (probably because I never used matrices so large). The error is likely related with the fact that double variables can exactly represent integers up to 2^53 only. The number of elements of your matrix does not exceed that limit, but it is near.

Maybe you can sidestep the issue, up to 2^53, by getting the row and column indices and then computing the linear index from those manually:

[ii,jj] = find(K);
inds = ii + (jj-1)*size(K,1);

If needed, you can push the limit up to 2^64 by using a uint64 linear index instead of double:

[ii,jj] = find(K);
inds = uint64(ii) + (uint64(jj)-1)*size(K,1);

Upvotes: 3

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