JGAP - simple question re evolve() and the fitness function evaluate()

In order to get a feel for the JGAP package I took a look at the
minimizing change code and wrote my own little test program.

I now have a question about evolve() and the fitness function
evaluate() I wrote.

If I have a population of 10, and call evolve(), shouldn't my fitness
function be called a constant time? I would think 10 times.

However, when I run my basic GA my evaluation function gets called
between 10 and 13 times .. I am not quite sure why this would happen.

Likewise if I set the number of evolutions to say 3, I'd expect my
fitness function evaluate() to be called 3 times as much as before, but
that doesn't happen either.

I suspect I do not understand the linkage between evolve and the
fitness function I defined.

Eventually I want to define my own crossover & mutation operators, but
I haven't gotten to the point.

Thanks,
Esmail

--------- sup****ting/additional information ----------------

Some sample output showing the variability in the number evaluate() is
called.


	(eval   1) x =   8  fitness = 56.00
	(eval   2) x =   9  fitness = 54.00
	(eval   3) x =   6  fitness = 54.00
	(eval   4) x =   0  fitness =  0.00
	(eval   5) x =  15  fitness =  0.00
	(eval   6) x =  13  fitness = 26.00
	(eval   7) x =   8  fitness = 56.00
	(eval   8) x =   8  fitness = 56.00
	(eval   9) x =  13  fitness = 26.00
	(eval  10) x =  11  fitness = 44.00

Best solution found:8


	(eval   1) x =   9  fitness = 54.00
	(eval   2) x =   0  fitness =  0.00
	(eval   3) x =  12  fitness = 36.00
	(eval   4) x =   2  fitness = 26.00
	(eval   5) x =   1  fitness = 14.00
	(eval   6) x =   5  fitness = 50.00
	(eval   7) x =   9  fitness = 54.00
	(eval   8) x =   6  fitness = 54.00
	(eval   9) x =   5  fitness = 50.00
	(eval  10) x =  10  fitness = 50.00
	(eval  11) x =   5  fitness = 50.00
	(eval  12) x =   6  fitness = 54.00
	(eval  13) x =   6  fitness = 54.00

Best solution found: 6


	(eval   1) x =  14  fitness = 14.00
	(eval   2) x =   6  fitness = 54.00
	(eval   3) x =   1  fitness = 14.00
	(eval   4) x =   6  fitness = 54.00
	(eval   5) x =  14  fitness = 14.00
	(eval   6) x =   1  fitness = 14.00
	(eval   7) x =   8  fitness = 56.00
	(eval   8) x =  13  fitness = 26.00
	(eval   9) x =  14  fitness = 14.00
	(eval  10) x =   6  fitness = 54.00
	(eval  11) x =  14  fitness = 14.00

Best solution found: 6




my short test source code to maximinze function 15x - x**2 over 0 to 15.
------------------------

im****t org.jgap.*;
im****t org.jgap.impl.*;

public class MyGA
{
     public static void main(String []args) throws Exception
     {
         final int MAX_EVOLUTIONS = 1;
         final int POP_SIZE = 10;
         final int LOW_RANGE = 0;
         final int HIGH_RANGE = 15;

         Configuration conf = new DefaultConfiguration();
         conf.setPreservFittestIndividual(true);  // elitism?
         // conf.setKeepPopulationSizeConstant(true); already done in
default 
config

         FitnessFunction myFunc = new MyFitness();
         conf.setFitnessFunction(myFunc);
         Gene sampleGene = new IntegerGene(conf, LOW_RANGE, HIGH_RANGE);
         IChromosome sampleChromosome = new Chromosome(conf, sampleGene,
1);

         conf.setSampleChromosome(sampleChromosome);
         conf.setPopulationSize(POP_SIZE);

         Genotype population = Genotype.randomInitialGenotype(conf);

         population.evolve(MAX_EVOLUTIONS);
         IChromosome bestSolutionSoFar =
population.getFittestChromosome();

         System.out.println("\nBest solution found: " +
                            bestSolutionSoFar.getGene(0).getAllele());

     }
}


------------------------

im****t org.jgap.FitnessFunction;
im****t org.jgap.IChromosome;

public class MyFitness extends FitnessFunction
{
	MyFitness()
	{
	}

	public double evaluate(IChromosome a_subject)
	{
		int x = (Integer) a_subject.getGene(0).getAllele();
		double ret_val = 15.0 * x - (x * x);
		System.out.printf("\t(eval %3d) x = %3d  fitness = %5.2f\n",
				          count++, x, ret_val);	
		return ret_val;
	}

	private int count = 1;
}