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how to find entropy of X.

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john karli 2018-12-22

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评论： john karli 2018-12-24

采纳的回答： Image Analyst

entropy.PNG
Book1.xlsx

how i implement this entropy formula(PNG file atached) in matlab code

my X is Column c in xlsx file(attached) i want to find for 1000 value

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John D'Errico 2018-12-22

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编辑：John D'Errico 2018-12-22

Why not just download the yalmip toolbox, which has entropy already implemented? Is here for download:

https://yalmip.github.io

john karli 2018-12-22

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i did't find

Walter Roberson 2018-12-23

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See the comments of

https://www.mathworks.com/matlabcentral/fileexchange/28692-entropy

there is an implementation in the comments .

There is a function in the image processing toolbox for the greyscale image case.

john karli 2018-12-23

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在 MATLAB Online 中打开

Thankx alot its work for me y = [1 -6011 -3000 2592]):

this code find the entropy

function [ent] = EntropyInt(y) 
% Calculate the entropy for an integer value of y 
% First verify that y is truely integer-valued 
Sum = sum(y); 
if( Sum ~= round(Sum) ) 
error('INTEGER_ENTROPY:InvalidInput', 'Input arguments must be of integer value.') 
end
% Generate the histogram 
[n x] = hist(y, double(min(y):max(y))); 
% Normalize the area of the histogram to make it a pdf 
n = n / sum(n); 
% Calculate the entropy 
indices = n ~= 0; 
ent = -sum(n(indices).*log2(n(indices))); 
end

john karli 2018-12-23

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indices = n ~= 0; i did't understand this line what does it mean

Image Analyst 2018-12-23

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log(0) is minus infinity, so n~= zero finds those bins where the value (number of counts in the histogram bin) is non-zero. So only those are passed into log2(), thus preventing a "-inf" result.

Walter Roberson 2018-12-23

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https://www.mathworks.com/help/matlab/math/array-indexing.html#d120e1410

john karli 2018-12-24

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thanks for your answer.. how can i find the join entropy ?

Image Analyst 2018-12-24

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What is that? Do you have a formula?

john karli 2018-12-24

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jointentroy.PNG

yes snap shot is attached kindly see

john karli 2018-12-24

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u got it??

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Image Analyst 2018-12-23

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You can try entropy() or entropyfilt() in the Image Processing Toolbox, if you have it. entropyfilt() does a sliding window computation of entropy whereas entropy does it for the whole array.