code: private double goldenMean(double a, double b) {
      if (geometric) {
        return a * Math.pow(b / a, GOLDEN_SECTION);
      } else {
        return a + (b - a) * GOLDEN_SECTION;
      }
    }
docs: The point that is the GOLDEN_SECTION along the way from a to b.
  a may be less or greater than b, you find the point 60-odd percent
  of the way from a to b.
  
  @param a Interval minimum
  @param b Interval maximum
  @return The GOLDEN_SECTION along the way from a to b.