Finding the difference between one idex and the remaining indices

Question

Michael 2018-1-8

回答： Michael 2018-1-9

I have a vector:

A = [1 2 3 4 5];

I want to find the difference between A(1) and the remaining indices:

A(1) = 1; 1 - A = [0 -1 -2 -3 -4]

I then want to continue to A(2) and until the end of the vector. So that I have the differenced between all points from each other.

At the moment I use loops but it is very time consuming. How can I do this using vectorization techniques to improve performance?

Many thanks! MATLAB 2016a

Answer 1

Michael 2018-1-9

If you're using 2016a or earlier, you'll want to use bsxfun:

>> A = [1 2 3 4 5]; >> bsxfun(@minus, A.', A) ans =

-1  -2  -3  -4
 0  -1  -2  -3
 1   0  -1  -2
 2   1   0  -1
 3   2   1   0

Starting in 2016b (or in Octave), you can take advantage of implicit expansion and do away with bsxfun:

>> A.' - A ans =

-1  -2  -3  -4
 0  -1  -2  -3
 1   0  -1  -2
 2   1   0  -1
 3   2   1   0