Hi Chaudhary,
As mentioned by Aman, you can index into the vector and multiply by a scalar:
indices = [2 4 6 8 10];
vector(indices) = vector(indices) * scalar;
This means that it doesn't have to be regular or follow any pattern i.e the index vector can contain any values and those indices will only be affected by the operation.
However, you have mentioned that you want to multiply at regular intervals. In case this interval is dynamic then you can use the semicolon ( : ) operator to generate the indices at the interval that you want.
Conside you have a variable n that you take as input. and then you want to multply the vector at every 3rd index till n i.e 3, 6, 9, ... n. In such cases consider the following:
n = 15; % This is input. Set to what you want
vector = [1 2 3 4 5 6 7 8 9 10 11 12 13 14 15]';
scalar = 10;
vector(3:3:n) = vector(3:3:n) * scalar;
% vector(start : offset : end ) is the usage
This solution will scale to vectors of any size and any interval constraints.
