How can I write this with a for loop?

r = (1/70).*( exp(i.*Y(:,3)) + exp(i.*Y(:,6)) + exp(i.*Y(:,9)) + exp(i.*Y(:,12)) + exp(i.*Y(:,15)) ...
    +exp(i.*Y(:,18)) +exp(i.*Y(:,21)) +exp(i.*Y(:,24)) + exp(i.*Y(:,27)) + exp(i.*Y(:,30)) + exp(i.*Y(:,33)) ...
    + exp(i.*Y(:,36)) + exp(i.*Y(:,39)) +exp(i.*Y(:,42)) + exp(i.*Y(:,45)) + exp(i.*Y(:,48)) + exp(i.*Y(:,51)) ...
    + exp(i.*Y(:,54))+ exp(i.*Y(:,57)) + exp(i.*Y(:,60)) + exp(i.*Y(:,63)) + exp(i.*Y(:,66)) + exp(i.*Y(:,69)) ...
    + exp(i.*Y(:,72)) + exp(i.*Y(:,75)) + exp(i.*Y(:,78)) + exp(i.*Y(:,81)) + exp(i.*Y(:,84)) + exp(i.*Y(:,87)) ...
    + exp(i.*Y(:,90)) + exp(i.*Y(:,93)) + exp(i.*Y(:,96)) + exp(i.*Y(:,99)) + exp(i.*Y(:,102)) + exp(i.*Y(:,105))...
    + exp(i.*Y(:,108)) + exp(i.*Y(:,111)) + exp(i.*Y(:,114))+ exp(i.*Y(:,117)) + exp(i.*Y(:,120)) + exp(i.*Y(:,123))...
    + exp(i.*Y(:,126)) + exp(i.*Y(:,129)) + exp(i.*Y(:,132)) + exp(i.*Y(:,135)) + exp(i.*Y(:,138)) + exp(i.*Y(:,141))...
    + exp(i.*Y(:,144)) + exp(i.*Y(:,147)) + exp(i.*Y(:,150)) + exp(i.*Y(:,153)) + exp(i.*Y(:,156)) + exp(i.*Y(:,159)) ...
    + exp(i.*Y(:,162)) + exp(i.*Y(:,165)) + exp(i.*Y(:,168)) + exp(i.*Y(:,171)) + exp(i.*Y(:,174)) + exp(i.*Y(:,177)) ...
    + exp(i.*Y(:,180)) + exp(i.*Y(:,183))+ exp(i.*Y(:,186)) + exp(i.*Y(:,189)) + exp(i.*Y(:,192)) + exp(i.*Y(:,195)) ...
    + exp(i.*Y(:,198)) + exp(i.*Y(:,201))+ exp(i.*Y(:,204)) + exp(i.*Y(:,207)) + exp(i.*Y(:,210)));

[Stephen23]

Why do you need to use a loop? Vectorized code would be simpler:

https://www.mathworks.com/help/matlab/matlab_prog/vectorization.html

Answer 1

[Dyuman Joshi]

Vectorization would be the best approach here -

r = (1./70).*sum(exp(i*Y(:,3:3:210)),2)

Answer 2

[Dr. W. Kurt Dobson]

Looks like the index you are using starts with 3, then increments by 3 up to 210.

Y looks like a matrix...

So, let's say the incrementing number is k, therefore you could do a for loop or just a vector computation.

For Loop Version (slower due to loop)
%
r = (1/70).*( exp(i.*Y(:,3));       % setup the first term
for k = 6:3:210                     % increment by three
    r = r + exp(i.*Y(:,k));         % for each term add, the prior to current   
end
%

Vector Version (much faster)
k = 6:3:210;                        % gen k vector start at 3, increment by 6 to 210
r = (1/70).*( exp(i.*Y(:,3));       % setup the first term
r = r + exp(i.*Y(:,k));             % vector calculation on remaining terms

[Dr. W. Kurt Dobson]

Oops, forgot a semicolon,

k = 6:3:210; % gen k vector start at 3, increment by 6 to 210

r = (1/70).*( exp(i.*Y(:,3))); % setup the first term

r = r + exp(i.*Y(:,k)); %