Construct a vector from another, but add 2 values every 10 iteration

Hello !

I would like to create a vector B from a vector A, and at every 10th iteration, implement 2 times the same value from A:

A = linspace(0,1,811);
B = [];

for i = 1:1:length(A)
    if mod(i,10) ~= 0 
        B = [B,A(1,i)]; 
    elseif   mod(i,10) == 0            
        added_value = A(1,i);
        B = [B,added_value,added_value];
    end
end

I know the length of the vector B should be around 901. I should have 90 "added_values", but when I verify it I have almost 1000 of them.

And it seems at every iteration the "if" condition just skips to the "elseif" part... What should I do to make this work ? I can't think of any other method...

Thanks in advance !

Answer 1

[Meg Noah]

Try this:

npts = 811;
A = linspace(0,1,npts);
numAdded = sum(mod(1:npts,10) == 0);
B = zeros(1,numAdded+npts);
k = 0;
for i = 1:1:npts
    k = k + 1;
    B(k) = A(1,i);
    
    if mod(i,10) == 0
        k = k + 1;
        B(k) = A(1,i);
    end
end

% another way to do it...
npts = 811;
A = linspace(0,1,npts);
idx = 1:npts;
idxRepeat = find(mod(1:npts,10) == 0);
idxA2B = sort([idx idxRepeat]);
B = A(idxA2B);

[V.D-C]

You just solved 2 days of intense failures, I can't thank you enough !!!