title: Choose m evenly spaced elements from a sequence of length n
body: <p>I have a vector/array of n elements. I want to choose m elements.</p>
  
  <p>The choices must be fair / deterministic -- equally many from each subsection.</p>
  
  <p>With m=10, n=20 it is easy: just take every second element.
  But how to do it in the general case? Do I have to calculate the LCD?</p>