A 'Hello World!' Genetic Algorithm Example in PHP

class Gac{
 
    const POPULATION_SIZE = 20;
    const MUTATION_RATE = 10;
    const MUTATION_SIZE = 100;
    const SURVIVORS = 10;
    const SUCCESS_RATE = 1;
    const LETTERS = "abcdefghijklmnopqrstuvwxyz ";
    const OFFSPRING = 2;
 
    public function Gac($text)
    {
        $this->text = $text;
        $this->lenght = strlen($this->text);
        $this->population = 0;
        $this->max_rate = 0;
        $this->avarage_suc_rate = 0;
        $this->best = array();
        $this->passed = FALSE;
        $this->generations = 0;
    }
 
    private function check_success($data)
    {
        $rate = 0;
 
        for($i=0;$i<$this->lenght;$i++)
        {
            $original_letter = substr($this->text,$i,1);
            $text_letter = substr($data,$i,1);
            if($original_letter == $text_letter)
            {
                $rate++;
            }
        }
 
        $rate = $rate/$this->lenght;
 
        return $rate;
    }
 
    private function first_population($gene_code)
    {
        $words = array();
        for($i=0;$i<self::POPULATION_SIZE;$i++)
        {
            $this->population++;
            $mutation = TRUE; //this is the first population, so mutate everything
 
            $new_ind = $this->generate($gene_code,$mutation);
            $words[$i]["word"] = $new_ind["word"];
            $words[$i]["rate"] = $new_ind["rate"];
            $words[$i]["gene_code"] = $new_ind["gene_code"];
 
            echo $new_ind["word"] . " - " . $new_ind["rate"] ."<br>\n";
 
        }
        echo "end of first generation <br>\n";
        echo "----------------------------<br>\n";
        array_unique($words);
        usort($words, "cmp");
        return $words;
    }
 
    private function kill($genes)
    {
        if(count($genes)>self::SURVIVORS)
        {
            $diff = count($genes) - self::SURVIVORS;
 
            for($i=0;$i<$diff;$i++)
            {
                array_pop($genes);
            }
 
            echo "killed $diff individuals<br>\n";
        }
 
        return $genes;
    }
 
    private function populate($genes)
    {
        $this->generations++;
        $new_genes = array();
        echo "------------ START OF " . $this->generations . " th GENERATION ----------------<br>\n";
        //cross everything
        usort($this->best,"cmp");
        for($j=0;$j<self::OFFSPRING;$j++)
        {
            for($i=0;$i<count($genes);$i++)
            {
                $this->population++;
                $best = FALSE;
 
                if($genes[$i]["rate"]>=$this->max_rate)
                {
                    $new_gene = $genes[$i]["gene_code"];
                    $best = TRUE;
                    echo "stay still<br>";
                }
                else
                {
                    if($genes[$i]["gene_code"]!==$genes[$i+1]["gene_code"] && $genes[$i+1]["gene_code"])
                    {
                        $new_gene = $this->cross($genes[$i]["gene_code"],$genes[$i+1]["gene_code"]);
                    }
                    else if($genes[$i]["gene_code"]!==$genes[$i+2]["gene_code"] && $genes[$i+2]["gene_code"])
                    {
                        $new_gene = $this->cross($genes[$i]["gene_code"],$genes[$i+2]["gene_code"]);
                    }
                    else
                    {
                        $new_gene = $genes[$i]["gene_code"];
                        echo "crossed nothing!<br>\n";
                    }
                }
 
                if($new_gene==$genes[$i]["gene_code"] && $i!==0)
                {
                    $new_gene = $this->mutate($new_gene);
                    echo "<span style='color:red'>mutated unexpectedly!</span><br>\n";
                }
 
                $mutation = FALSE;
 
                if($this->population % self::MUTATION_SIZE == 0)
                {
                    //mutate the new created gene if the mutation size reached
                    echo "mutation<br>\n";
                    $mutation = TRUE;
                }
 
                $new_ind = $this->generate($new_gene,$mutation);
                $new_genes[$i]["word"] = $new_ind["word"];
                $new_genes[$i]["rate"] = $new_ind["rate"];
                $new_genes[$i]["gene_code"] = $new_ind["gene_code"];
 
                if($new_ind["rate"]>=$this->max_rate && !in_array($new_ind,$this->best) )
                {
                    $this->max_rate = $new_ind["rate"];
                    $this->best[] = $new_ind;
                    usort($this->best,"cmp");
                }
 
                echo $new_ind["word"] . " - " . $new_ind["rate"] ."<br>\n";
            }
        }
 
 
        array_unique($new_genes);
        usort($new_genes, "cmp");
        return $new_genes;
    }
 
    private function cross($gene1,$gene2)
    {
        $new_gene = array();
        for($i=0;$i<$this->lenght;$i++)
        {
            $rand = rand(0,1);
            if($rand)
            {
                $new_gene[$i] = $gene1[$i];
            }
            else
            {
                $new_gene[$i] = $gene2[$i];
            }
        }
 
        if($new_gene !== $gene1 && $new_gene !== $gene2)
        {
            echo "<span style='color:green'>cross successfull </span><br>";
        }
 
        return $new_gene;
    }
 
    public function execute()
    {
        //the first gene code
        $gene_code = $this->generate_gene_code();
        $first_population = $this->first_population($gene_code);
        $result = $this->evolution($first_population);
 
        return $result;
    }
 
    private function evolution($genes_data)
    {
        //return $genes_data;
        if($genes_data[0]["rate"]>=self::SUCCESS_RATE)
        {
            echo $genes_data[0]["word"]. " found after ". $this->population . " try";
            return $genes_data;
        }
        else
        {
            if(count($this->best)>self::SURVIVORS || $this->passed)
            {
                usort($this->best,"cmp");
                $this->best = $this->kill($this->best);
                $genes = $this->best;
                $this->passed = TRUE;
            }
            else
            {
                $genes = $genes_data;
            }
            return $this->evolution($this->populate($genes));
        }
    }
 
    private function generate_gene_code()
    {
        $code = array();
        for($i=0;$i<$this->lenght;$i++)
        {
            $code[] = rand(0,strlen(self::LETTERS));
        }
        return $code;
    }
 
    private function generate($gene_code,$mutation)
    {
        //generates new individuals according to genetic code
        if($mutation)
        {
            $gene_code = $this->mutate($gene_code);
        }
 
        $new_word = "";
 
        for($i=0;$i<$this->lenght;$i++)
        {
            $letter = substr(self::LETTERS,$gene_code[$i],1);
            $new_word .= $letter;
        }
 
        $new_ind = array();
 
        $new_ind["gene_code"] = $gene_code;
        $new_ind["word"] = $new_word;
        $new_ind["rate"] = $this->check_success($new_word);
 
        return $new_ind;
    }
 
    private function mutate($gene_code)
    {
        //mutate original data and returns it
        $mutate_letter_num = floor(self::MUTATION_RATE * $this->lenght / 100);
        $mutate_letters = array();
 
        for($i=0;$i<$mutate_letter_num;$i++)
        {
            $which = rand(0,$this->lenght-1);
            $mutate_letters[] = $which;
        }
 
        array_unique($mutate_letters);
 
        foreach($mutate_letters as $letter_num)
        {
            $gene_code[$letter_num] = rand(0,strlen(self::LETTERS));
        }
        return $gene_code;
    }
}

set_time_limit(0);
ini_set("memory_limit","256M");
function cmp($a, $b)
{
    if ($a["rate"] == $b["rate"]) {
        return 0;
    }
    return ($a["rate"] > $b["rate"]) ? -1 : 1;
}
 
include("gac.php");
 
$text = "hello world";
$my_ga = new Gac($text);
 
 
$first_gene_code = $my_ga->execute();