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corr2 return 1 for different value

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khalida basheer
khalida basheer 2020-9-20
评论： khalida basheer 2020-9-21
why when i use corr2 for different value in matlab return result=1 although the tow matrix not similar like this:-
aa
aa =
137.5093 1.9847
>> bb
bb =
141.2252 3.3757
>> corr2(aa,bb)
ans =
1

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回答（1 个）

Ameer Hamza
Ameer Hamza 2020-9-20
If you use only 2D vectors with corr2(), it is always possible to draw a line connecting two points, so the correction coefficient is always 1 or -1. You can verify this by simplifying the formula: https://www.mathworks.com/help/releases/R2020a/images/ref/corr2.html#f1-227958 for the case when x and y are 2D vectors.
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Walter Roberson
Walter Roberson 2020-9-21
If you try something like
[H,p] = ttest2(aa,bb)
you will get a p > 0.9 -- that is, if you treat the numbers as being a random distribution, there is more than a 90% chance that they come from the same random distribution.
The large value of the second feature dilutes the variation in the other features. If you take the correlation with the second feature removed, you will get a notably lower score. Perhaps you should rescale the second feature.
khalida basheer
khalida basheer 2020-9-21
Sir Walter Roberson, actually the problem is the second feature, after deleting it and relying on other features, I got the acceptable result
thank you very much

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