# Find doesn't seem to work with Matrix larger than 127x127

2 views (last 30 days)
Bartosz on 28 Jan 2023
Commented: Walter Roberson on 28 Jan 2023
[i,j]=find(A);
A is matrix of size n where n varies in size from 100 to 2000 (each time calculation is completed it's incremented by 50). For n = 100 all is fine, but once I reach 150 i and j only record values to 127.
If it is relevant A is matrix of adjacency for complete binary tree of n nodes
Bartosz on 28 Jan 2023
Thanks, problem has been solved. Sorry for your wasted time on such a simple mistake of mine

Walter Roberson on 28 Jan 2023
I am certain that find works. I speculate that you are putting the values together in an array with values of datatype int8. When you put together values of mixed data type, the output result is typically the most restricted data type of all of the inputs.
Walter Roberson on 28 Jan 2023
I would suggest that your code would probably be clearer if you were to build A as being n by 2 by something -- you could reshape it back afterwards.

Jan on 28 Jan 2023
This observation does not match the facts:
X = randi([0, 1], 150, 150);
[i,j] = find(X);
max(i)
ans = 150
max(j)
ans = 150
If you observe a very strange behavior, which implies, that hundrets of thousands Matlab users did not notice a serious problem in standard function for many years, you can be sure, that your observation is wrong.
If no indices > 127 are found in your case, there are no non-zeros with such indices. The limit of 127 sounds like the maximum value of int8 values.
Please post some code, which reproduces the problem. I'm sure, that the proble ist not the find() command, but hidden in your code.

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