how to reverse a random permutation of a matrix to get back the original matrix?

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shashwat soni
shashwat soni 2018-9-17
评论： shuaib ahmed 2019-6-13
O = key1(randperm(numel(key1)));
here O is the random permutation of rows and columns of a 'key1' matrix which is '16*147'. how to get back my original key1 matrix?

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采纳的回答

Andrei Bobrov
Andrei Bobrov 2018-9-17
key1 = randi(398,4,5);
s = size(key1);
p = reshape(randperm(numel(key1)),s);
O = key1(p);
[~,ii] = sort(p(:));
out = O(reshape(ii,s));

更多回答（1 个）

Image Analyst
Image Analyst 2018-9-17
See attached demo.
  2 个评论
shashwat soni
shashwat soni 2018-9-17
in my case the image(original) matrix is a 2d matrix, now i want to generate 3 random integers for each element of a row in the matrix, for e.g. if my matrix is 16*49, so i want a 16*147(147 = 49*3) matrix so that each element of a row in the original matrix gives me 3 random elements. And again i should be able to decrypt it
Image Analyst
Image Analyst 2018-9-17
My code would give 16*49 numbers, which would keep each pixel together. In other words, the green and blue values move to the same location as the red value. This has the effect of simply shuffling the pixels to new locations while keeping the color of the pixel the same (because red, green, and blue all move together to the same new location).
I'm not sure if you want 3 values for each row, or if you want 3 values for each pixel - you seemed to say/indicate both. If you wanted 3 values for each row, I'm not sure how that would look. If you wanted 3 values for each pixel then you could be moving the red, green, and blue values to different locations. To do that with my code you'd simply get 3 sort orders, one for each color channel:
% Get the orders to scramble them in.
scrambleOrderR = randperm(rows*columns);
scrambleOrderG = randperm(rows*columns);
scrambleOrderB = randperm(rows*columns);
% Scramble according to the scrambling order for each individual color channel.
redChannel = redChannel(scrambleOrderR);
greenChannel = greenChannel(scrambleOrderG);
blueChannel = blueChannel(scrambleOrderB);

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