code: public RandomVariable getImpliedBachelierATMOptionVolatility(RandomVariable optionValue, double optionMaturity, double swapAnnuity){
  		return optionValue.average().mult(Math.sqrt(2.0 * Math.PI / optionMaturity) / swapAnnuity);
  	}
docs: Calculates ATM Bachelier implied volatilities.
  
  @see net.finmath.functions.AnalyticFormulas#bachelierOptionImpliedVolatility(double, double, double, double, double)
  
  @param optionValue RandomVarable representing the value of the option
  @param optionMaturity Time to maturity.
  @param swapAnnuity The swap annuity as seen on valuation time.
  @return The Bachelier implied volatility.