Incremental matrix without loop

Question

(Just approaching Matlab for personal understanding), suppose I have a Z,Y matrix in this case Z=1 Y=3

A=1:3

output: 1 2 3

Now I need to increase the matrix vertically to obtain:

1 2 3
2 4 6
3 6 9

How can I achieve that without using a loop?

Federico · Accepted Answer · 2015-04-26T12:22:24.227

4

The easiest way is to use vector multiplication.

If your goal is to obtain

1 2 3
2 4 6
3 6 9

given A=1:3

all you have to do is

A.'*A

This will take the vector product of the transpose (.') of A with A itself

edited Apr 26 '15 at 12:22

answered Apr 24 '15 at 13:28

Federico

Thanks a lot. Appreciated. – FeliceM Apr 24 '15 at 13:30
1

well you explicitly wrote **transpose** - the transpose operator is `.'` - the `'` is the conjugate transpose. Though it doesn't matter in this case, its not entirely correct as it stands. [**It is just a matter of clean programming**](http://stackoverflow.com/questions/25150027/using-transpose-versus-ctranspose-in-matlab). – Robert Seifert Apr 26 '15 at 12:15
1

@thewaywewalk then please accept my apologies, I never seen that difference. reinstating your edit. – Federico Apr 26 '15 at 12:22

score 2 · Answer 2 · answered Apr 24 '15 at 14:58

2

Another way is to use bsxfun:

A = [1 2 3];
B = bsxfun(@times, A.', A);

This is essentially the same answer as Federico's where the outer product of the vector is taken.

answered Apr 24 '15 at 14:58

rayryeng

1

If you benchmark, this might be the winner approach you know! – Divakar Apr 25 '15 at 08:42
@Divakar - heh heh heh, of course you'd say that :)! – rayryeng Apr 25 '15 at 08:51
Comeon, it's not just my love for bsxfun speaking! :) – Divakar Apr 25 '15 at 08:52

2 Answers2