Second and third sigma of standard devition.

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James
James 2014-4-21
评论： Sean de Wolski 2014-4-21
Hi,
I have a big 200x1 matrix "A" and want to find the standard deviations of it. I know that the Std(x)gives you the first sigma. How do you find the second and third sigma of "A" in Matlab. I am very interested in those as whell for this data.
Thanks
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dpb
dpb 2014-4-21
For what definition of "second and third sigma"? You mean the higher moments, maybe? If so and have Statistics Toolbox
doc moment
If not, compute as you would the std deviation if didn't have the function std except using the chosen moment for the power instead of 2.

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Image Analyst
Image Analyst 2014-4-21
For what it's worth, attached here is some code to find up through the 4th central moments: mean, std, var, skewness, kurtosis. The data can be any array - doesn't need to be an image.
By the way, 200 elements is not "big", it's microscopic. Now if you had 200 million elements, then that would be big (at this point in time).
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Sean de Wolski
Sean de Wolski 2014-4-21
200 million is still pretty manageable locally, on my relatively wimpy laptop:
Now 200 billion :)

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