13) ) 
					continue;
				else
				{
					$bOperator		= false;
					$buffer[$cBuff++] = $this_gene;
					continue;
				}
			}
			
			//find a gene which represents a number
			else
			{
				if ($this_gene > 9)
					continue;
				else
				{
					$bOperator		= true;
					$buffer[$cBuff++] = $this_gene;
					continue;
				}
			}
			
		}//next gene
	
		//	now we have to run through buffer to see if a possible divide by zero
		//	is included and delete it. (ie a '/' followed by a '0'). We take an easy
		//	way out here and just change the '/' to a '+'. This will not effect the 
		//	evolution of the solution
		for ($i=0; $i < $cBuff; $i++)
		{
			if (($buffer[$i] == 13) && ($buffer[$i + 1] == 0))
				$buffer[$i] = 10;
		}
	
		return $cBuff;
	}
	
	function AssignFitness($bits, $target_value)
	{
	
		//holds decimal values of gene sequence
		$buffer = array((int)(CHROMO_LENGTH / GENE_LENGTH));
	
		$num_elements = ParseBits($bits, $buffer);
		
		// ok, we have a buffer filled with valid values of: operator - number - operator - number..
		// now we calculate what this represents.
		$result = 0.0;
	
		for ($i=0; $i < $num_elements-1; $i+=2)
		{
			switch ($buffer[$i])
			{
				case 10:
	
					$result += $buffer[$i + 1];
					break;
	
				case 11:
					
					$result -= $buffer[$i + 1];
					break;
	
				case 12:
	
					$result *= $buffer[$i + 1];
					break;
	
				case 13:
		
					$result /= $buffer[$i + 1];
					break;
	
			}//end switch
	
		}
	
		// Now we calculate the fitness. First check to see if a solution has been found
		// and assign an arbitarily high fitness score if this is so.
	
		if ($result == (float)$target_value)
	
			return 999.0;
	
		else
	
			return 1/(float)abs((double)($target_value - $result));
		//	return result;
	}

	
	// chromosome Class
	class chromo
	{
		var $bits;
		var $fitness;
		
		function chromo($start_bits = "", $start_fitness = 0.0)
		{
			$this->bits = $start_bits;
			$this->fitness = $start_fitness;
		}
		
		function GetRandomBits()
		{
			// clear the bits
			$this->bits = "";
			
			for($i = 0; $i < CHROMO_LENGTH; $i++)
			{
				$r = rand(0, RAND_MAX) / (RAND_MAX + 1);
				//echo $r."
";
				if($r > 0.5)
					$this->bits .= "1";
				else
					$this->bits .= "0";
			}
		}
		
		function ToDec($start = 0, $stop = 0)
		{
			$val = 0;
			$value_to_add = 1;
		
			// convert the whole string
			if($start == $stop)
			{
				for ($i = strlen($this->bits); $i > 0; $i--)
				{
					if ($this->bits[($i - 1)] == '1')
						$val += $value_to_add;

					$value_to_add *= 2;
				}
			}
			else
			{
				$str = substr($this->bits, $start, $stop);
				for ($i = strlen($str); $i > 0; $i--)
				{
					if ($str[($i - 1)] == '1')
						$val += $value_to_add;
			
					$value_to_add *= 2;
				}
			}
			return $val;
		}
		
		function PrintChromo()
		{	
			//holds decimal values of gene sequence
			$buffer = array((int)(CHROMO_LENGTH / GENE_LENGTH));
			
			//parse the bit string
			$num_elements = ParseBits($this->bits, &$buffer);
			
			for ($i=0; $i < $num_elements; $i++)
		 	{
				PrintGeneSymbol($buffer[$i]);
			}
			return;
		}
	
	} // end class chromo
	
	function Mutate($bits = "")
	{
		for ($i=0; $i < strlen($bits); $i++)
		{
			if ((rand(0, RAND_MAX) / (RAND_MAX + 1)) < MUTATION_RATE)
			{
				if ($bits[$i] == '1')
					$bits[$i] = '0';
				else
					$bits[$i] = '1';
			}
		}
		
		return;
	}
	
	function Crossover(&$offspring1, &$offspring2)
	{
		  //dependent on the crossover rate
		if ((rand(0, RAND_MAX) / (RAND_MAX + 1)) < CROSSOVER_RATE)
		{
			//create a random crossover point
			$crossover = (int) ((rand(0, RAND_MAX) / (RAND_MAX + 1)) * CHROMO_LENGTH);
			$t1 = substr($offspring1, 0, $crossover) . substr($offspring2, $crossover, CHROMO_LENGTH);
			$t2 = substr($offspring2, 0, $crossover) . substr($offspring1, $crossover, CHROMO_LENGTH);
		
			$offspring1 = $t1; $offspring2 = $t2;				  
		}
	}
	
	function Roulette($total_fitness, &$Population)
	{
		//generate a random number between 0 & total fitness count
		$Slice = (float)((rand(0, RAND_MAX) / (RAND_MAX + 1)) * $total_fitness);
		
		//go through the chromosones adding up the fitness so far
		$FitnessSoFar = 0.0;
		
		for ($i = 0; $i < POP_SIZE; $i++)
		{
			$FitnessSoFar += $Population[$i]->fitness;
			
			//if the fitness so far > random number return the chromo at this point
			if ($FitnessSoFar >= $Slice)
	
				return $Population[$i]->bits;
		}
		
		return "";
	}
	
	function BinToDec($bits)
	{
		$val = 0;
		$value_to_add = 1;
	
		for ($i = strlen($bits); $i > 0; $i--)
		{
			if ($bits[($i - 1)] == '1')
	
				$val += $value_to_add;
	
			$value_to_add *= 2;
		
		}
	
		return $val;
	}

	function PrintGeneSymbol($val)
	{
	if ($val < 10 )
		echo  $val." ";
	else
	{
		switch ($val)
		{
		case 10:
			 "+";
			break;
		case 11:
			echo "-";
			break;
		case 12:
			echo "*";
			break;
		case 13:
			echo "/";
			break;
		}//end switch
		echo " ";
	}

	return;
	}	

	$Population = array(POP_SIZE);
	for ($i=0; $iGetRandomBits();
		$Population[$i]->fitness = 0.0;
	}
	
	$GenerationsRequiredToFindASolution = 0;
	
	 $bFound = false;

	while(!$bFound)
	{
		$TotalFitness = 0.0;
		
		for($i=0; $ifitness = AssignFitness($Population[$i]->bits, $Target);
			$TotalFitness += $Population[$i]->fitness;
		}
	
		 // check to see if we have found any solutions (fitness will be 999)
		for ($i=0; $ifitness == 999.0)
			{
				echo "Solution found in ".$GenerationsRequiredToFindASolution." generations!
";
				$Population[$i]->PrintChromo();
				$bFound = true;
         		break;
			}
		}

		$temp = array(POP_SIZE);
		for ($i=0; $iGetRandomBits();
			$temp[$i]->fitness = 0.0;
		}
		$cPop = 0;
	  
		  //loop until we have created POP_SIZE new chromosomes
		while ($cPop < POP_SIZE)
		{
			// we are going to create the new population by grabbing members of the old population
			// two at a time via roulette wheel selection.
			$offspring1 = Roulette($TotalFitness, $Population);
			$offspring2 = Roulette($TotalFitness, $Population);

        	//add crossover dependent on the crossover rate
        	Crossover($offspring1, $offspring2);

			//now mutate dependent on the mutation rate
			Mutate($offspring1);
			Mutate($offspring2);

			//add these offspring to the new population. (assigning zero as their
        	//fitness scores)
			$temp[$cPop++] = new chromo($offspring1, 0.0);
			$temp[$cPop++] = new chromo($offspring2, 0.0);
		}//end loop

		for ($i=0; $i MAX_ALLOWABLE_GENERATIONS)
		{
			echo "No solutions found this run!";
			$bFound = true;
		}

	}
?>