code: public static double toGrowthRateFromAnnualReturn(double annualReturn, CalendarDateUnit growthRateUnit) {
          double tmpAnnualGrowthRate = PrimitiveMath.LOG1P.invoke(annualReturn);
          double tmpYearsPerGrowthRateUnit = CalendarDateUnit.YEAR.convert(growthRateUnit);
          return tmpAnnualGrowthRate * tmpYearsPerGrowthRateUnit;
      }
docs: GrowthRate = ln(1.0 + InterestRate) / GrowthRateUnitsPerYear
  
  @param annualReturn Annualised return (percentage per year)
  @param growthRateUnit A growth rate unit
  @return A growth rate per unit (day, week, month, year...)