Find differences in a set of points without a for loop

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Sonoma Rich
Sonoma Rich 2015-4-21
评论： Image Analyst 2022-5-19
I a vector of numbers that I am trying to find the differences between each element in the vector without a for loop. Below is a code example. Is there a more efficient way to execute this code without a for loop?
x = rand(20,1);
diff = zeros(length(x),length(x));
for ix = 1:length(x)
for iy = (ix+1):length(x)
diff(ix,iy) = abs(x(ix) - x(iy));
end
end

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回答（3 个）

Image Analyst
Image Analyst 2015-4-21
编辑：Image Analyst 2015-4-21
diff() is a built in function. Don't use it for a variable name.
For a microscopic length such as 20, don't worry about a for loop. It won't take any time at all, and in fact may take less than calling some fancy function.
  1 个评论
Image Analyst
Image Analyst 2015-4-21
Richard's "Answer" moved here since it is not an answer to the original question:
Thanks for the help. My actual code has a vector that is much larger. I was just using this as an example.

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Mehri Mehrnia
Mehri Mehrnia 2022-5-19
I have the question to find all pair-wise difference in a group without loop!
My array in scale of milions!
Bruno Luong
Bruno Luong 2022-5-19
编辑：Bruno Luong 2022-5-19
Ran in:
x = randi(10,3,1)
x = 3×1
5 4 8
d = abs(x - x.')
d = 3×3
0 1 3 1 0 4 3 4 0

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