code: public static List<MutableDoubleTuple> normalize(
          Collection<? extends DoubleTuple> inputs,
          List<MutableDoubleTuple> results)
      {
          results = validate(inputs, results);
          int index = 0;
          for (DoubleTuple input : inputs)
          {
              MutableDoubleTuple result = results.get(index);
              DoubleTuples.normalize(input, result);
              index++;
          }
          return results;
      }
docs: Normalize the given collection of {@link MutableDoubleTuple}s.<br>
  <br>
  The results will be written into the given result tuples.
  If the given results list is <code>null</code>, then a new
  list will be created and returned. <br>
  <br>
  If the result list is not <code>null</code>, then it must have the
  same size as the input collection, otherwise an
  <code>IllegalArgumentException</code> will be thrown.<br>
  <br>
  If the input collection contains <code>null</code> elements, then a
  <code>NullPointerException</code> will be thrown. <br>
  <br>
  If the result list contains <code>null</code> elements, then a
  <code>NullPointerException</code> will be thrown. <br>
  <br>
  The input collection and the results list may contain
  pairwise identical elements.<br>
  <br>
  The input collection and the results list may be identical.
  <br>
  
  @param inputs The tuples to normalize
  @param results The result tuples
  @return The result tuples
  @throws IllegalArgumentException If the result list is not
  <code>null</code> and has a size that is different from the size
  of the input collection
  @throws NullPointerException If the inputs list is <code>null</code>
  or contains <code>null</code> elements, or if the output list is
  non-<code>null</code> and contains <code>null</code> elements
  @see DoubleTuples#normalize(DoubleTuple, MutableDoubleTuple)