Modifying odd/even numbers of a column vector

How would I go about modifying the odd and even elements of the following vector ?

x = [4 5 7 6 5 8 2 1];

So that when run it can carry out either +,-,*,/,^ ?.

Also after the vectors have been changed the disp(x); shows all all elements, including ones not changed.

Answer 1

[Rik]

If you have trouble with Matlab basics you may consider doing the Onramp tutorial (which is provided for free by Mathworks).

x = [4 5 7 6 5 8 2 1];

%with simple indexing:
x(1:2:end)=2*x(1:2:end);
disp(x);

     8     5    14     6    10     8     4     1

%or with logical indexing with mod:
L=mod(x,2)==0;
x(L)=2*x(L);
disp(x);

    16     5    28    12    20    16     8     1

[Matt Smith]

Thank you!

Answer 2

[Hernia Baby]

You can modyfiy each element with mod function.

x = [4 5 7 6 5 8 2 1];
x_odd   = x(mod(x,2)==1); % odd element
x_even  = x(mod(x,2)==0); % even element

mod

https://jp.mathworks.com/help/matlab/ref/mod.html

[Matt Smith]

Thanks for you reply!

This seperates the vector, which is not what I want.

Say for example I wanted to multiply just the odd elements by 2. I'd want the other elements to not be affected but still displayed like this:

x = [4 5 7 6 5 8 2 1];

disp(x);
4 10 14 6 10 8 2 2

[Rik]

Note that you made a small typo: you should have used == to compare the output of mod to 1 or 0.

[Hernia Baby]

Thank you, Rik! I will modify my typo.

--------------------------------

To Matt

I got what you want to do.

Then, you can do this with logical indexing.

It is same with Rik's code.

times = 2;
x = [4 5 7 6 5 8 2 1];
idx_odd   = mod(x,2) == 1; % odd element

x(idx_odd) = times * x(idx_odd);
disp(x);