How to subtract elements in a matrix

Hello,

I have a matrix and I need to subtract every element from each other in each row. So, for example, if I have a matrix A=[1 2 3; 4 8 9] the result should be for example this B=[1 2 1; 4 5 1] - the sequence is not important. But I need to know that the result in the matrix B corresponds to a particular elements' subtraction in matrix A. So if I have for example a subtraction of 2-1, which is A(1,2)-A(1,1) in matrix A and the result is 1 in matrix B I need to know that 1 corresponds to A(1,2)-A(1,1) and keep track of it.

I have tried to do it with cycles and also with a "bsxfun" function but unfortunately can't get the correct result.

g=[1 3 8; 4 6 2];

[u,v]=size(g);

      for i=1:u
          for j=1:v
      a(i,j)=bsxfun(@minus,g(i,j),g(i,j)');
          end
      end

I'll be glad if anyone can help me. Thanks

[KL]

A has 1 2 and 3 in first row. If you say " I need to subtract every element from each other in each row".. then that means 1-2-3 for the first element, 2-1-3 for the second element, 3-2-1 for the thir element. But your B looks totally different. What exactly do you mean?

[Jakub Nosek]

Yes, exactly. I need to do 1-2-3, 2-1-3 and 3-2-1 and the same in other rows but I suppose that for example 1-2 and 2-1 is the same as it will be an absolute value.

[KL]

It's still not consistent with your expected result in B! Your A is

 A = [1 2 3; 4 8 9];

and your expected B is

 B = [1 2 1; 4 5 1];

if you want to subtract every element from each other (even if you store the absolute value), your B should rather be,

 B = [4 2 0; 13 5 3]

Do you understand?

[Jakub Nosek]

Well, there must be a misunderstanding. Sorry about that. Let's say we have A=[1 2 3; 4 8 9] Now I want to do this: 1-2, 1-3, 2-3 and 4-8,4-9,9-8

In a real matrix that I want to use, the elements are aircraft's altitudes and thus the columns are individual aircraft and rows times in which the altitudes were measured. I need to continuously check the altitude separation between all aircraft. Hence I need to calculate the altitude differences in every time step.

Answer 1

[Roger Stafford]

You don't need a for-loop.

C = nchoosek(1:size(A,2),2);
B = A(:,C(:,2))-A(:,C(:,1));

[Jakub Nosek]

Thanks a lot! This works!

Answer 2

[KL]

Ok, I guess you want to subtract following column with the current column,

 B = circshift(A,-1,2)-A

But your expected B rather looks like the result of,

 B = [A(:,2)-A(:,1) A(:,3)-A(:,1) A(:,3)-A(:,2)]