indexing using for loop

I have a column vector with 480 values. I am asked to do the following:

Find the number of singular values required to capture at least 90% of the variance, i.e. the smallest index such that the value in the vector is greater than 0.90.

I don't really understand what this means/how to do it. I was told that you can somehow use a for loop and if statement to compute this, but I don't even understand what this is asking and how to go about that.

Answer 1

[Akira Agata]

Of course you can do it with using for loop and if statement. But MATLAB can do it much better way like this:

x = rand(480, 1);
x = sort(x); % column vector with 480 values

idx = find(x > 0.9, 1); % smallest index such that x > 0.9

If you want to use for loop and if statement, the code becomes much longer, such as:

x = rand(480, 1);
x = sort(x); % column vector with 480 values

for kk = 1:480
  if x(kk) > 0.9
      idx = kk; % smallest index such that x > 0.9
      break;
  end
end