Addition to specified elements in a vector with for loop to create a new vector

Hi all,

I am trying to add to specified elements in a vector to create a new one with the new values, however, unfortunately I could not make it...

The addition has been made to all the elements!

clear all;
x=[-7.5 -2.5 2.5 7.5]  % 
for i=1:3
    xx(1,i)=2.5+x(i) % I need the 2.5 added only to [-7.5 -2.5 2.5] and also I need the output to be with the original vector included 
    % I mean I'd like the output to be 
    % xx(1,i)= [-7.5 -5 -2.5 0 2.5 5 7.5]
    % I know i only = 3 and I need the output to be 9 elements but what can I do ??
    
end

[Korbinian Volgt]

I am not sure what your exact intention is by +2.5, I guess what you want is to have an equally distributed vector with a step of 2.5 instead of 5. In general it's good practice to predefine vectorlength, so one approach would be:

x=[-7.5 -2.5 2.5 7.5];
xx = zeros(1,7);
for i=1:3
  xx(1,2*i-1) = x(1,i);
  xx(1,2*i) = x(1,i) + 2.5;
end
xx(1,end) = x(end)

But much easier would be to define your vector as equal distributed numbers from your minimum to the maximum value with the stepsize of 2.5:

xx = -7.5:2.5:7.5

[Ali Tawfik]

Hi Korbinian,

actually david has answered what I meant, however,I have been trying to have output of 9 elements because later I will use this vector in plot...

I mean I need some of the elements to be repeated like the following:

[-7.5 -5 -2.5 -2.5 0 2.5 2.5 5 7.5]

Hope you understand, and try to help me!

Answer 1

[David Hill]

xx=[x(1:3);x(1:3)+2.5];
xx=[xx(:)',x(4:end)];

[Ali Tawfik]

Hi David,

it's totally fine, but may I ask you for something more:, actually I'd like to have output of 9 elements because later I will use this vector in plot...

I mean I need some of the elements to be repeated like the following:

[-7.5 -5 -2.5 -2.5 0 2.5 2.5 5 7.5]

Hope you understand, and try to help me!

[David Hill]

What elements to you want repeated? I don't understand what you are trying to do. What are you plotting against?

[Ali Tawfik]

Hi,

Thanks for your prompt reply.

I will plot them aganist vector of 9 elements, I would like to repeat element no#: 3 and 6

so it's -2.5 and 2.5.