public boolean setRates(double[] rates)
    {
        // error checking
        if (rates == null || rates.length != numClasses_) {
            return false;
        }

        // the value of each rate must be a positive number
        for (int i = 0; i < rates.length; i++)
        {
            if (rates[i] <= 0)
            {
                System.out.println(super.get_name() +
                    ".setRates(): Error - the rate must be a positive number.");
                return false;
            }
        }

        this.rates_ = rates;
        return true;
    }