How to select the columns of a matrix which are a multiple of 5?

Hye

I don't know how to solve the following exercise:

M is a 3x5000 matrix. A student wants to select the elements on the third row in all columns which are a multiple of 5.

The student writes the following script.

N = zeros(1,1000)
for i = 1:5000
    if rem(i,5) == 0
        N(i/5) = M(3,i);
    end
end 

I have to simplify it using only N = M(...). How do I do that?

[Guillaume]

It's hard to give you any help without giving the solution away (which would be cheating).

For which i values would the if be true? Couldn't you pass these values directly as indices of M and not bother with the loop?

Answer 1

[Alex Mcaulley]

N = M(3,5:5:end)

[Guillaume]

In my opinion (as an academic), it'd be better if you didn't post outright solution to homework. Particularly, when it's that easy.

[Alex Mcaulley]

Oops you are right, I didn't realise it was homework

Answer 2

[Ellen De Jonghe]

Hi guys, thanks a lot for your help!

I managed to solve exercises which are way more difficult, but my mind is still full of my previous exam stuff, so I didn't see that the solution ofr this case was so simple. Hope that makes sense ;)