Simple Question about Optimization of a FOR loop

How can I optimize (vectorize?) the following code in order to avoid the for loop and make the code to run faster?

    for i=1:55;
        A(i)=B((i-1)*3+1,1);
    end

A is 1 x 55 and B is 165 x 1

Many thanks!

[Matt Kindig]

This loop will make A only 1x55, not 55x55.

[Laila Kazemi]

bc ur only assigning one raw to A

[Mohsen]

You are both right!

A is 1 x 55

Do you know how to optimize the for loop? Thanks!

Answer 1

[Laila Kazemi]

C= B*3 +1 A (1:55, 1:55)= C(1:55, 1)

but the dimensions of ur matrices dont match , if B was 55 by 1 , it would have worked

[Laila Kazemi]

C= B*3 +1

A (1:55, 1:55)= C(1:55, 1)

[Laila Kazemi]

actaully instead one make a matrix called D with D( , 1:165)=(1)

[Mohsen]

Thanks for your answer but it doesn't seem to be the right answer... Please note that the multiplication by 3 and the addition by 1 is used to access the content of each element and not to modify the content of the elements...

I found this answer and it worked:

A=B(1:3:55*3,1);

Thanks again.

Answer 2

[Andrei Bobrov]

A(1,:) = B((0:size(A,2)-1)*3+1);

[Mohsen]

Thanks for your answer but it doesn't seem to be the right answer...

I found this answer and it worked:

A=B(1:3:55*3,1);

Thanks again.