Easy way to multiplying standard basis
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It seems to be easy, but I am not good at it.
I would like to generate the following matrix that is multiplying of two standard basis:
E_{ij}:= (e_i - e_j)(e_i - e_j)^T
Could any body knows how to write it in few lines?
Thanks
6 Comments
Azzi Abdelmalek
on 22 Feb 2013
Edited: Azzi Abdelmalek
on 22 Feb 2013
It seems that second Wayne's answer is what you are looking for
Answers (3)
Thiru jeyan
on 2 May 2017
You can use this method
e=@(k,n) [zeros(k-1,1);1;zeros(n-k,1)]
For an example
>> e(1,3)
ans =
1 0 0
>> e(2,5)
ans =
0 1 0 0 0
0 Comments
Wayne King
on 22 Feb 2013
I agree with the comment above that you should provide an example because it's not clear what the size of your problem is or how scalable you want it. For example, are you looking for something as simple as:
E1 = [1 0 0]';
E2 = [0 1 0]';
matrx = (E1-E2)*(E1-E2)';
1 Comment
Wayne King
on 22 Feb 2013
You can just do
I = eye(5);
Each column of I is a standard basis vector
Then,
idx = [3 4];
Is = I(:,idx(1))-I(:,idx(2));
X = Is*Is';
gives you what you want for an example where i=3 and j= 4
2 Comments
Wayne King
on 22 Feb 2013
so just extract the columns, what is so difficult about that?
Did you look at the Is vector? that is just a column vector.
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