static IF1<Double> growFactorXinYDays(double x, double y, double valueAtDayZero default 1.0) {
  ret new IF1<Double> {
    public Double get(Double day) {
      ret valueAtDayZero*pow(x, day/y);
    }
    
    toString {
      ret jreplace_multi_gen("valueAtDayZero*pow(x, day/y)",
        +valueAtDayZero, +x, +y);
    }
  };
}