code: public double density(double x) {
          if (means != null)
              throw new IllegalStateException("Unable to sample from more than one mean");
          final double x0 = x - mean;
          final double x1 = x0 / standardDeviation;
          return FastMath.exp(-0.5 * x1 * x1) / (standardDeviation * SQRT2PI);
      }
docs: {@inheritDoc}