How can i find indices of constant elements between 2 arrays?

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Hi, i have 2 enormous matrices A and B which are parameter relevant. With find() function i know which elements are non zero and with find(A-B) i know which elements are changed due to parameter. But how can i find out the indices of elements which remain constant?
  4 Comments
Jiahong Zou
Jiahong Zou on 31 May 2023
Edited: Image Analyst on 31 May 2023
Yeah sure. For example,
A = [1 2 0; 0 1 0; 5 0 8]
A = 3×3
1 2 0 0 1 0 5 0 8
B = [ 1 3 0; 0 4 0; 5 0 6]
B = 3×3
1 3 0 0 4 0 5 0 6
How to find the indices of bold 1 and 5 ? Zero elements must be not included, because i tried
[row_zero, column_zero] = find(~(A - B))
row_zero = 6×1
1 2 3 3 1 2
column_zero = 6×1
1 1 1 2 3 3
And it directly went out of memory.
Image Analyst
Image Analyst on 31 May 2023
Exactly how big are your arrays? Hundreds of millions of elements or more?

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Accepted Answer

the cyclist
the cyclist on 31 May 2023
Do you mean the non-zero elements that are the same between the two arrays?
A = [1 2 0; 0 1 0; 5 0 8];
B = [1 3 0; 0 4 0; 5 0 6];
[r,c] = find(A==B & A~=0)
r = 2×1
1 3
c = 2×1
1 1

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