code: public static double toGrowthFactorFromAnnualReturn(double annualReturn, CalendarDateUnit growthFactorUnit) {
          double tmpAnnualGrowthFactor = PrimitiveMath.ONE + annualReturn;
          double tmpYearsPerGrowthFactorUnit = CalendarDateUnit.YEAR.convert(growthFactorUnit);
          return PrimitiveMath.POW.invoke(tmpAnnualGrowthFactor, tmpYearsPerGrowthFactorUnit);
      }
docs: GrowthFactor = exp(GrowthRate)
  
  @param annualReturn Annualised return (percentage per year)
  @param growthFactorUnit A growth factor unit
  @return A growth factor per unit (day, week, month, year...)