code: public static MutableLongTuple addScaled(
          LongTuple t0, long factor, LongTuple t1, 
          MutableLongTuple result)
      {
          return LongTupleFunctions.apply(
              t0, t1, (a,b)->(a+factor*b), result);
      }
docs: Computes <code>t0+factor*t1</code>, and stores the result in the given
  result tuple.
  
  @param t0 The first input tuple
  @param factor The scaling factor
  @param t1 The second input tuple
  @param result The tuple that will store the result
  @return The result tuple
  @throws IllegalArgumentException If the given tuples do not
  have the same {@link Tuple#getSize() size}