Thread Subject: Reciprocal of a column?

Hello,
I am still very new to Matlab and I'm having a little problem.
I have a large Matrix and I want to add a column that is the reciprocal of another column I already have.

For example, I create a Matrix A: [3; 2; 1]
Then I want to create a second column which has the reciprocal of those values.

I tried:

A(:,2) = 1/A(:,1)

but that results in a seceond column of [0.33333 , 0 , 0]', so obviously something went wrong here.
The line A(1:3,2) = 1/A(1:3,2) gives the same result.

So I guess my question really is, what syntax do I have to use so that the correct value gets calculated in every row, because obviously the way I tried it doesn't work.

Sorry if this question seems pretty dumb, I couldnt really find the answer in the Matlab help and it would be really nice if you could clear this up for me or point me in the right direction.

Thanks,
Christian

Christian wrote:
...
> For example, I create a Matrix A: [3; 2; 1]
> Then I want to create a second column which has the reciprocal of those values.
>
> I tried:
>
> A(:,2) = 1/A(:,1)
>
...

 >> a=[a, 1./a(:,1)]
a =
     3.0000 0.3333
     2.0000 0.5000
     1.0000 1.0000

doc horzcat

--

"Christian " <vlad.impotech@gmx.net> wrote in message <hej5dt$ela$1@fred.mathworks.com>...
> Hello,
> I am still very new to Matlab and I'm having a little problem.
> I have a large Matrix and I want to add a column that is the reciprocal of another column I already have.
>
> For example, I create a Matrix A: [3; 2; 1]
> Then I want to create a second column which has the reciprocal of those values.
>
> I tried:
>
> A(:,2) = 1/A(:,1)
>
> but that results in a seceond column of [0.33333 , 0 , 0]', so obviously something went wrong here.
> The line A(1:3,2) = 1/A(1:3,2) gives the same result.
>
> So I guess my question really is, what syntax do I have to use so that the correct value gets calculated in every row, because obviously the way I tried it doesn't work.
>
> Sorry if this question seems pretty dumb, I couldnt really find the answer in the Matlab help and it would be really nice if you could clear this up for me or point me in the right direction.
>
> Thanks,
> Christian

Hi Christian, you should read about Matlab's . operator, is this context, you can see

>>help rdivide

A= [3; 2; 1];
A(:,2) = 1./A(:,1);

Hope that helps,
Wayne

Thank you guys for the super-quick answers.
I can absolutely see my problem now. I just didnt know about that operator and how to use it, but now it's all clear :)